Decoding 1998 Jeep Grand Cherokee OBD2 Codes: Your Comprehensive Guide

Navigating the complexities of vehicle diagnostics can be daunting, especially when your trusty 1998 Jeep Grand Cherokee flashes that perplexing check engine light. Understanding OBD2 codes is crucial for any owner looking to maintain their vehicle’s peak performance and address issues efficiently. This guide serves as your definitive resource for deciphering 1998 Jeep Grand Cherokee Obd2 Codes, ensuring you’re equipped with the knowledge to diagnose problems and get back on the road with confidence.

Understanding OBD2 Systems in Your 1998 Jeep Grand Cherokee

The 1998 Jeep Grand Cherokee, like many vehicles of its era, utilizes an OBD2 (On-Board Diagnostics II) system. This standardized system is designed to monitor various aspects of your vehicle’s engine and emissions systems. When the system detects a problem, it triggers the check engine light and stores a diagnostic trouble code (DTC). These codes are your car’s way of communicating specific issues, from minor sensor malfunctions to more significant engine problems.

OBD2 systems were a significant advancement over earlier diagnostic systems, offering a more comprehensive and standardized approach to vehicle troubleshooting. For 1998 Jeep Grand Cherokee owners, understanding these codes is the first step in effective vehicle maintenance and repair. By accessing and interpreting these codes, you can pinpoint the source of the problem, potentially saving time and money on unnecessary repairs.

1998 Jeep Grand Cherokee OBD2 Code List: Carbureted Engines

While the 1998 Jeep Grand Cherokee primarily used fuel-injected engines, some earlier models or variations might have featured carbureted engines. For those less common configurations, here’s a list of OBD codes that could be relevant:

CODE 12: No distributor reference pulses to the ECM. This indicates an issue with the signal from the distributor to the Engine Control Module (ECM). This code is usually transient and may appear when the ignition is on but the engine isn’t running. It suggests a problem with the distributor, wiring, or ECM.
CODE 13: Oxygen sensor circuit. This code signals a problem with the oxygen sensor circuit. The system needs to run for a period under normal driving conditions to set this code, indicating the importance of driving patterns in diagnostics. This could be due to a faulty sensor, wiring issues, or exhaust leaks.
CODE 14: Shorted coolant sensor circuit. A short circuit in the coolant temperature sensor system. Like code 13, this requires engine operation to be detected. Possible causes include a faulty sensor, shorted wiring, or ECM issues.
CODE 15: Open coolant sensor circuit. An open circuit in the coolant temperature sensor system, also requiring engine operation for detection. This could be due to a disconnected sensor, broken wiring, or sensor failure.
CODE 21: Throttle position sensor circuit. Indicates a problem with the throttle position sensor (TPS) circuit. This code sets after a period of idling, highlighting the importance of idle conditions in TPS diagnostics. Potential issues are a faulty TPS, wiring problems, or incorrect TPS adjustment.
CODE 23: Mixture control solenoid circuit is shorted or open. This points to a malfunction in the mixture control solenoid circuit, affecting fuel-air mixture regulation in carbureted engines. This could be due to a faulty solenoid, wiring problems, or ECM issues.
CODE 34: Vacuum sensor circuit. A problem within the vacuum sensor circuit. This code sets after a period of idling, similar to code 21, emphasizing idle condition relevance. Possible causes include a faulty vacuum sensor, vacuum leaks, or wiring problems.
CODE 41: No distributor reference pulses to the ECM at the specified engine manifold vacuum. Similar to code 12, but specifically under manifold vacuum conditions and is stored in memory, indicating a more persistent issue. This suggests a problem with the distributor signal under load or vacuum conditions.
CODE 42: Electronic Spark Timing (EST) bypass circuit or EST circuit has short circuit to ground or an open circuit. Indicates issues with the electronic spark timing system, crucial for engine performance. This could be due to wiring shorts, open circuits, or ECM problems related to spark timing control.
CODE 44: Lean exhaust indication. The system detects a lean exhaust condition, meaning too much oxygen in the exhaust. This requires closed loop operation and part throttle driving to set. Possible causes include vacuum leaks, fuel delivery problems, or faulty oxygen sensor.
CODE 44 & 45: If these two codes appear together, it strongly indicates a problem specifically within the oxygen sensor circuit itself, rather than just rich or lean conditions. This points directly to the oxygen sensor or its wiring as the primary suspect.
CODE 45: Rich exhaust indication. The system detects a rich exhaust condition, meaning too much fuel in the exhaust. Similar conditions to code 44 are needed for this code to set, but indicating the opposite fuel-air mixture problem. Possible causes include fuel injector issues, faulty pressure regulator, or air intake restrictions.
CODE 51: Faulty calibration unit (PROM) or installation. Indicates a problem with the Programmable Read-Only Memory (PROM) chip in the ECM. This code can take up to 30 seconds to set, suggesting a processing or memory related issue. This is often related to ECM failure or incorrect PROM installation.
CODE 54: Mixture Control (MC) solenoid circuit is shorted or the ECM is faulty. Similar to code 23, but also implicates the ECM as a potential cause. This broadens the possible fault to include both the solenoid and the ECM itself.
CODE 55: Voltage reference has short circuit to ground (terminal 21), faulty oxygen sensor or faulty ECM. A general voltage reference issue, which could stem from a short circuit, a faulty oxygen sensor impacting the reference voltage, or a faulty ECM. This is a more general error suggesting a fundamental electrical or sensor problem.

1998 Jeep Grand Cherokee OBD2 Code List: Fuel Injected Engines (Pre-1996 Models)

For 1998 Jeep Grand Cherokees equipped with fuel-injected engines, understanding the specific code ranges is essential. While the original document mentions “Except 1991 and Later Models” which is confusing for a 1998 vehicle, we should interpret this section as applying to pre-OBD2 standardized fuel injection codes, which are less relevant for a 1998 model but are included for completeness based on the original source material. It’s important to note that for a 1998 Jeep Grand Cherokee, the P-codes (P0xxx) listed in the “1996 and Later Models” section are the most relevant and accurate. However, for historical context and to align with the original source, we list these older codes:

Code 1000-1073 & 1200-1223: These codes represent a wide range of potential issues related to the fuel injection system and various sensors and circuits. They cover problems like ignition line voltage (high/low), oxygen sensor heater circuit, battery voltage issues, sensor ground problems, diagnostic enable line faults, MAP sensor issues (high/low), fuel pump circuit malfunctions, charge air temperature sensor problems (high/low), lack of serial data from the ECU, engine starting failures, throttle position sensor readings (high/low), idle speed control issues, coolant temperature sensor problems (high/low), knock sensor circuit faults, A/C system related electrical issues, oxygen sensor readings (rich/lean), latch relay problems, speed sensor signal absence, ECU defects, injector circuit faults (shorted/open), and voltage supply issues to the ECU.

It’s crucial to understand that for a 1998 Jeep Grand Cherokee, these numerical codes (1000-1223) are less likely to be directly applicable compared to the standardized P-codes. Modern OBD2 scanners will primarily report P-codes.

1998 Jeep Grand Cherokee OBD2 Code List: 1996 and Later Models (P-Codes)

This section contains the most relevant OBD2 codes for a 1998 Jeep Grand Cherokee, as it aligns with the OBD2 standardization era (1996 onwards) and uses the standard P-code format. These codes are what you will most likely encounter when using an OBD2 scanner on your 1998 Jeep Grand Cherokee.

P0107 – Manifold Absolute Pressure/Barometric Pressure Circuit Low Input: Indicates the MAP/BARO sensor is reporting lower than expected pressure values. This can be caused by a sensor malfunction, wiring issues, or vacuum leaks.
P0108 – Manifold Absolute Pressure/Barometric Pressure Circuit High Input: The MAP/BARO sensor is reporting higher than expected pressure values. Potential causes include sensor failure, wiring problems, or a blockage in the sensor’s pressure port.
P0112 – Intake Air Temperature Circuit Low Input: The IAT sensor is reporting a lower than expected air temperature. This could be due to a faulty sensor, shorted wiring, or ECM issues.
P0113 – Intake Air Temperature Circuit High Input: The IAT sensor is reporting a higher than expected air temperature. Possible causes include a faulty sensor, open wiring, or ECM problems.
P0117 – Engine Coolant Temperature Circuit Low Input: The ECT sensor is reporting a lower than expected coolant temperature. This could be caused by a faulty sensor, shorted wiring, or low coolant levels.
P0118 – Engine Coolant Temperature Circuit High Input: The ECT sensor is reporting a higher than expected coolant temperature. Potential causes include a faulty sensor, open wiring, or overheating issues.
P0121 – Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance Problem: Indicates the TPS signal is not within the expected range or is not changing as expected with throttle movement. This could be due to a faulty TPS, poor connection, or throttle body issues.
P0122 – Throttle/Pedal Position Sensor/Switch A Circuit Low Input: The TPS is reporting a lower than expected voltage. Possible causes include a faulty TPS, shorted wiring, or poor connection.
P0123 – Throttle/Pedal Position Sensor/Switch A Circuit High Input: The TPS is reporting a higher than expected voltage. Potential causes include a faulty TPS, open wiring, or ECM issues.
P0125 – Insufficient Coolant Temperature for Closed Loop Fuel Control: The engine is not reaching the required coolant temperature for the system to enter closed loop operation (optimal fuel efficiency and emissions control). This is often related to a thermostat issue or a faulty ECT sensor.
P0129 – Catalyst Monitor Slow O2 Sensor (Bank 1 Sensor 2): Indicates the downstream oxygen sensor (sensor 2 on bank 1) is responding too slowly during catalyst monitoring. This suggests a potential issue with the oxygen sensor or the catalytic converter’s efficiency.
P0131 – Left Bank and Upstream O2 Sensor Voltage Shorted to Ground: The upstream oxygen sensor on bank 1 is shorted to ground, causing a low voltage reading. This could be due to wiring damage or a faulty sensor.
P0132 – Left Upstream O2 Sensor Shorted to Voltage: The upstream oxygen sensor on bank 1 is shorted to voltage, causing a high voltage reading. This could be due to wiring issues or a faulty sensor.
P0133 – Upstream O2 Sensor Circuit Slow Response (Bank 1 Sensor 1): The upstream oxygen sensor on bank 1 is responding slower than expected to changes in exhaust gas composition. This indicates a failing or contaminated oxygen sensor.
P0135 – O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1): The heater circuit for the upstream oxygen sensor on bank 1 is malfunctioning. The heater is crucial for the sensor to reach operating temperature quickly. This could be due to a faulty sensor, wiring issues, or a blown fuse.
P0137 – Left Bank Downstream or Downstream and Pre-catalyst O2 Sensor Voltage Shorted to Ground: The downstream oxygen sensor (or downstream and pre-catalyst sensor) on bank 1 is shorted to ground. Similar to P0131, but for the downstream sensor.
P0138 – Left Bank Downstream or Downstream and Pre-catalyst O2 Sensor Shorted to Voltage: The downstream oxygen sensor (or downstream and pre-catalyst sensor) on bank 1 is shorted to voltage. Similar to P0132, but for the downstream sensor.
P0141 – Downstream, Left Bank Downstream or Pre-catalyst O2 Sensor Heater Failure: The heater circuit for the downstream oxygen sensor (or downstream/pre-catalyst sensor) on bank 1 is failing. Similar to P0135, but for the downstream sensor.
P0152 – Left Upstream O2 Sensor Slow Response: Another code indicating a slow response from the upstream oxygen sensor on bank 1. Similar to P0133, but may indicate a different type of sensor issue.
P0162 – Charging System Voltage Too Low: The system voltage is too low, potentially affecting various sensors and systems. This is often related to a weak battery, alternator problems, or voltage regulator issues.
P0171 – Right Rear (or just) Fuel System Too Lean: The fuel system is running lean, meaning there’s too much air and not enough fuel in the mixture. This could be due to vacuum leaks, fuel delivery problems, or a faulty MAF sensor.
P0172 – Left Bank or Fuel System Too Rich: The fuel system is running rich, meaning there’s too much fuel and not enough air in the mixture. Possible causes include fuel injector leaks, a faulty fuel pressure regulator, or air intake restrictions.
P0201 – P0208 – Injector No. 1 – No. 8 Control Circuit: These codes (one for each injector) indicate a problem with the control circuit for a specific fuel injector. This could be due to a faulty injector, wiring problems, or ECM issues.
P0300 – Random/Multiple Cylinder Misfire Detected: The engine is experiencing misfires in multiple cylinders or in a random pattern. This could be caused by ignition problems, fuel delivery issues, vacuum leaks, or compression problems.
P0301 – P0308 – Cylinder No. 1 – No. 8 Misfire Detected: These codes (one for each cylinder) indicate a misfire in a specific cylinder. Possible causes are similar to P0300 but specific to a cylinder.
P0320 – No Crank Reference Signal PCM: The PCM is not receiving a crank reference signal, which is crucial for ignition and fuel injection timing. This is often related to a faulty crankshaft position sensor, wiring issues, or ECM problems.
P0340 – No Cam Signal at PCM: The PCM is not receiving a camshaft position sensor signal. This is important for engine synchronization and can be caused by a faulty camshaft position sensor, wiring issues, or timing chain/belt problems.
P0351 – Ignition Coil No. 1 Primary Circuit: Indicates a problem with the primary circuit of ignition coil number 1. This could be due to a faulty coil, wiring issues, or ECM problems.
P0420 – Left Bank Catalytic Converter or Just Catalytic Converter Efficiency Failure: The catalytic converter efficiency is below the acceptable threshold. This could be due to a failing catalytic converter, exhaust leaks, or engine problems causing excessive emissions.
P0441 – Evaporative Purge Flow Monitor Failure: The evaporative emission (EVAP) purge flow is not functioning correctly. This could be due to a faulty purge solenoid, vacuum leaks in the EVAP system, or blockage.
P0442 – Evaporative Emission Control System Leak Detected (Small Leak): A small leak is detected in the EVAP system. This could be due to a loose gas cap, cracked hoses, or faulty EVAP components.
P0443 – Evap Purge Solenoid Circuit: A problem in the EVAP purge solenoid circuit. This could be due to a faulty solenoid, wiring issues, or ECM problems.
P0455 – Evaporative Emission Control System Leak Detected (Gross Leak): A large leak is detected in the EVAP system. Similar causes to P0442, but a more significant leak.
P0460 – Fuel Level Unit No Change Over Miles: The fuel level sensor signal is not changing as expected over a distance driven. This could be due to a faulty fuel level sensor, wiring issues, or a problem with the instrument cluster.
P0462 – Fuel Level Sending Unit Voltage Too Low: The fuel level sensor is reporting a lower than expected voltage. This could be due to a faulty sensor, shorted wiring, or a low fuel level.
P0463 – Fuel Level Sending Unit Voltage Too High: The fuel level sensor is reporting a higher than expected voltage. This could be due to a faulty sensor, open wiring, or a full fuel tank.
P0500 – No Vehicle Speed Sensor Signal: The vehicle speed sensor (VSS) signal is absent. This can affect speedometer function, transmission shifting, and cruise control. It could be due to a faulty VSS, wiring problems, or instrument cluster issues.
P0505 – Idle Air Control Motor Circuits: Problems within the idle air control (IAC) motor circuits. This can cause idle speed issues (too high or too low). Potential causes include a faulty IAC motor, wiring problems, or vacuum leaks.
P0600 – PCM/Serial Communication Link Malfunction: A malfunction in the communication link to the Powertrain Control Module (PCM). This indicates a serious communication problem within the vehicle’s electronic systems.
P0601 – Internal Controller Failure: Indicates an internal failure within the PCM itself. This often requires PCM replacement.
P0622 – Generator Field Not Switching Properly: The generator (alternator) field is not switching as expected, indicating a charging system problem. This could be due to a faulty alternator, voltage regulator issues, or wiring problems.
P0645 – A/C Clutch Relay Circuit: A problem in the air conditioning (A/C) clutch relay circuit. This can prevent the A/C compressor from engaging. Potential causes include a faulty relay, wiring issues, or A/C system problems.
P0711 – Transmission Fluid Temperature Sensor, No Temperature Rise After Start: The transmission fluid temperature sensor is not showing a temperature increase after starting the vehicle. This could be due to a faulty sensor or actual transmission temperature issues.
P0712 – Transmission Fluid Temperature Sensor Voltage Too Low: The transmission fluid temperature sensor is reporting a lower than expected voltage. This could be due to a faulty sensor or shorted wiring.
P0713 – Transmission Fluid Temperature Sensor Voltage Too High: The transmission fluid temperature sensor is reporting a higher than expected voltage. This could be due to a faulty sensor or open wiring.
P0720 – Low Output Speed Sensor RPM Above 15 MPH: The output speed sensor is reporting low RPM while the vehicle is moving above 15 MPH. This indicates a problem with the output speed sensor or transmission function.
P0740 – Torque Converter Clutch, No RPM Drop at Lockup: The torque converter clutch is not locking up as expected, or there’s no RPM drop when it should lock. This can affect fuel economy and transmission performance. Potential causes include a faulty torque converter clutch solenoid or transmission issues.
P0743 – Torque Converter Clutch Solenoid/Trans Relay Circuits: Problems in the torque converter clutch solenoid or transmission relay circuits. This can prevent the torque converter clutch from engaging or disengaging.
P0748 – Governor Pressure Solenoid Control/Trans Relay Circuits: Problems in the governor pressure solenoid control or transmission relay circuits. This affects transmission pressure control and shifting.
P0751 – Overdrive Switch Pressed (LO) More Than 5 Minutes: The overdrive switch is detected as being pressed (low) for an extended period. This could be due to a stuck switch or wiring issues.
P0753 – Trans 3-4 Shift Solenoid/Trans Relay Circuits: Problems in the 3-4 shift solenoid or transmission relay circuits. This can affect 3rd to 4th gear shifting.
P0783 – 3-4 Shift Solenoid, No RPM Drop @ 3-4 Shift: Similar to P0753, but specifically indicating no RPM drop during a 3-4 shift, pointing to a 3-4 shift solenoid issue.
P1195 – Catalyst Monitor Slow O2 Sensor (Bank 1 Sensor 1): Similar to P0133, indicating a slow response from the upstream oxygen sensor during catalyst monitoring.
P1197 – Catalyst Monitor Slow O2 Sensor (Bank 1 Sensor 2): Similar to P0129, indicating a slow response from the downstream oxygen sensor during catalyst monitoring.
P1281 – Engine is Cold Too Long: The engine is taking too long to reach operating temperature. This is often related to a thermostat problem.
P1282 – Fuel Pump Relay Control Circuit: A problem in the fuel pump relay control circuit. This can prevent the fuel pump from operating correctly.
P1294 – Target Idle Not Reached: The engine is unable to reach the target idle RPM. This could be due to vacuum leaks, IAC motor issues, or throttle body problems.
P1296 – No 5 Volts to MAP Sensor: The MAP sensor is not receiving the necessary 5-volt reference voltage. This could be due to wiring issues or PCM problems.
P1297 – No Change in MAP from Start to Run: The MAP sensor reading is not changing from engine start to running conditions. This could indicate a faulty MAP sensor or vacuum leaks.
P1388 – Auto Shutdown Relay Control Circuit: A problem in the auto shutdown (ASD) relay control circuit. The ASD relay is crucial for providing power to the ignition and fuel systems.
P1389 – No ASD Relay Output Voltage at PCM: The PCM is not detecting output voltage from the ASD relay. This indicates a problem with the ASD relay or its circuit.
P1391 – Intermittent Loss of CMP or CKP: Intermittent loss of camshaft position (CMP) or crankshaft position (CKP) sensor signals. This can cause engine stalling or misfires.
P1398 – Misfire Adaptive Numerator at Limit or No Crank Sensor Learn: Indicates a misfire issue related to adaptive learning limits or a problem with crank sensor learning.
P1486 – EVAP Leak Monitor Pinched Hose or Obstruction Found: The EVAP leak monitor system has detected a pinched hose or obstruction in the EVAP system.
P1492 – Battery Temp Sensor Voltage Too High: The battery temperature sensor is reporting a higher than expected voltage. This could be due to a faulty sensor or wiring issues.
P1493 – Battery Temp Sensor Voltage Too Low: The battery temperature sensor is reporting a lower than expected voltage. This could be due to a faulty sensor or wiring issues.
P1494 – Leak Detection Pump Pressure Switch or Mechanical Fault: A problem with the leak detection pump pressure switch or a mechanical fault within the leak detection pump system of the EVAP system.
P1495 – Leak Detection Pump Solenoid Circuit: A problem in the leak detection pump solenoid circuit.
P1594 – Charging System Voltage Too High: The charging system voltage is too high. This could be due to a faulty voltage regulator or alternator problems.
P1595 – Speed Control Solenoid Circuits: Problems in the speed control (cruise control) solenoid circuits.
P1596 – Speed Control Switch Always High: The speed control switch is always reporting a high signal. This could be due to a stuck switch or wiring issues.
P1597 – Speed Control Switch Always Low: The speed control switch is always reporting a low signal. This could be due to a stuck switch or wiring issues.
P1683 – Speed Control Power Circuit: A problem in the speed control power circuit.
P1696 – PCM Failure EEPROM Write Denied: The PCM is experiencing an EEPROM write failure, indicating a potential PCM memory issue.
P1698 – PCM Failure EEPROM Write Denied: Similar to P1696, another indication of a PCM EEPROM write failure.
P1756 – Governor Pressure Not Equal to Target @ 15-20 PSI: The transmission governor pressure is not matching the target pressure at 15-20 PSI. This indicates a transmission pressure control problem.
P1757 – Governor Pressure Above 3 PSI in Gear with 0 MPH: The governor pressure is too high (above 3 PSI) when in gear and at 0 MPH. This points to a transmission governor or pressure control issue.
P1762 – Governor Pressure Sensor Offset Volts Too Low or High: The governor pressure sensor offset voltage is out of range (too low or too high). This indicates a faulty pressure sensor.
P1763 – Governor Pressure Sensor Volts Too High: The governor pressure sensor is reporting a higher than expected voltage. This could be due to a faulty sensor or wiring issues.
P1764 – Governor Pressure Sensor Volts Too Low: The governor pressure sensor is reporting a lower than expected voltage. This could be due to a faulty sensor or wiring issues.
P1765 – Trans 12 Volts Supply Relay Control Circuit: A problem in the transmission 12-volt supply relay control circuit. This can affect transmission operation.
P1899 – P/N Switch Stuck in Park or in Gear: The Park/Neutral (P/N) switch is indicating that the vehicle is stuck in Park or in Gear, even when it’s not. This can affect starting and transmission operation.

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How to Use OBD2 Codes to Diagnose Your 1998 Jeep Grand Cherokee

Once you have retrieved the OBD2 code from your 1998 Jeep Grand Cherokee using a scanner, the next step is diagnosis. Here’s a general approach:

Record the Code: Write down the exact code and any freeze frame data provided by the scanner. Freeze frame data captures engine parameters at the moment the code was triggered, which can be valuable for diagnosis.
Research the Code: Use this guide or other reliable resources to understand the meaning of the code and potential causes.
Visual Inspection: Check for obvious issues like loose gas caps, vacuum leaks (hoses), and wiring damage around the affected sensor or system.
Component Testing: Depending on the code, you may need to test specific components like sensors, solenoids, or relays. A multimeter and a repair manual can be helpful for this step.
Systematic Troubleshooting: Follow a logical process of elimination. Start with the most likely and easiest-to-check causes, and proceed to more complex possibilities.
Clear the Code and Retest: After addressing the suspected issue, clear the OBD2 code using your scanner and take your Jeep for a test drive. See if the code returns. If it does, continue troubleshooting.

Important Note: While OBD2 codes provide valuable clues, they don’t always pinpoint the exact problem. Further investigation and testing are often necessary for accurate diagnosis and repair.

Conclusion

Understanding and utilizing OBD2 codes is an empowering skill for any 1998 Jeep Grand Cherokee owner. This guide provides a comprehensive list of codes, their meanings, and general diagnostic steps to help you tackle check engine light issues effectively. By being proactive in diagnosing and addressing these codes, you can ensure the longevity, performance, and reliability of your 1998 Jeep Grand Cherokee. Remember to always consult a qualified mechanic if you are unsure about any diagnosis or repair procedure.