Understanding the diagnostic system in your 1999 Chevy Monte Carlo is crucial for effective car maintenance and repair. If you’re trying to figure out the OBD2 pin count for your vehicle, you’ve come to the right place. This guide will clarify the details surrounding the diagnostic connector in your 1999 Chevy Monte Carlo, helping you identify the system and proceed with any necessary diagnostics.
The late 1990s was a transition period for automotive diagnostic systems, particularly for General Motors (GM) vehicles. During this time, some models, including the 1999 Chevy Monte Carlo, could be equipped with what’s often referred to as OBD 1.5. This hybrid system blends characteristics of both OBD1 and OBD2, which can sometimes lead to confusion.
One of the most straightforward ways to initially differentiate between these systems is by examining the Diagnostic Link Connector (DLC), commonly known as the OBD port. The number of pins in this connector is a key indicator.
Identifying Your Connector: Pin Count is Key
To determine whether your 1999 Chevy Monte Carlo leans towards an OBD1 or OBD2 system in terms of its connector, the first step is to count the number of pins in your DLC.
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12-Pin Connector: OBD1 Style System – If your 1999 Chevy Monte Carlo has a 12-pin DLC, it’s likely operating with a system that is fundamentally based on OBD1 protocols, even if it has some advancements. These systems typically require different diagnostic procedures compared to full OBD2.
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16-Pin Connector: OBD2 Style Port (Potentially OBD 1.5) – A 16-pin DLC is the standard for OBD2 systems. The 1999 Chevy Monte Carlo, while having this 16-pin OBD2-style port, might still operate on a transitional OBD 1.5 system. This means while the physical connector is OBD2-like, the underlying communication and diagnostic protocols might not be fully OBD2 compliant.
Where to Locate and Count the Pins
The DLC in a 1999 Chevy Monte Carlo is typically located under the dashboard on the driver’s side. You’ll usually find it in the vicinity of the steering column or the center console area.
- Locate the DLC: Look for a trapezoidal-shaped connector, usually black or dark grey, beneath the dash on the driver’s side.
- Visually Inspect the Pins: Once you’ve located the connector, take a close look at the front of it. You will be able to see the small metallic pins inside the connector.
- Count the Pins: Carefully count the number of pins within the connector. This count will determine whether you have a 12-pin or 16-pin configuration.
Diagnosing a 1999 Chevy Monte Carlo with a 16-Pin Connector (OBD 1.5 Scenario)
If your 1999 Chevy Monte Carlo has a 16-pin connector, but you suspect it might be running an OBD 1.5 system, reading diagnostic codes can be slightly different from a standard OBD2 vehicle.
The “Paper Clip” or Jumper Wire Method for OBD 1.5
For OBD 1.5 systems, a common method to retrieve diagnostic trouble codes (DTCs) involves using a jumper wire or a paper clip to bridge specific terminals within the DLC. This method relies on the vehicle’s computer flashing the “Check Engine” light in a pattern to represent the codes.
How to Use the Jumper Wire Method:
- Locate Terminals A and B: On the 16-pin DLC, identify terminal A and terminal B. These are typically the top right and the terminal directly below it on many GM vehicles, but consulting a specific pinout diagram for the 1999 Chevy Monte Carlo is always recommended for accuracy.
- Prepare a Jumper Wire: Take a small length of wire or an unfolded paper clip to act as your jumper.
- Turn Off the Ignition: Ensure the vehicle’s ignition is turned completely off.
- Bridge Terminals A and B: Carefully insert the jumper wire to connect terminal A and terminal B within the DLC.
- Turn the Ignition to “ON” (Do Not Start the Engine): Turn the ignition key to the “ON” position, but do not start the engine.
- Observe the “Check Engine” Light: Watch the “Check Engine” light on your dashboard. It will begin to flash a series of codes.
Interpreting the Flash Codes:
The codes are flashed in a sequence. A code is represented by a series of flashes: a long flash represents “10” and a short flash represents “1”. The codes are typically two-digit codes. For example, code 12 is flashed as one long flash followed by two short flashes.
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Code 12 (System Normal): Code 12 is often the first code to flash and is generally considered a system check code, indicating the diagnostic system is functioning. It can usually be ignored when diagnosing a specific problem, and you should focus on subsequent codes.
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Example Code Reading:
- Code 12: Long flash, short flash, short flash.
- Code 13: Long flash, short flash, short flash, short flash.
Common GM OBD1 Codes (Pre-1995 and Potentially Applicable to OBD 1.5):
While the 1999 Chevy Monte Carlo is newer than 1995, understanding common OBD1 codes can still be helpful, especially if you suspect an OBD 1.5 system. Here’s a list of frequently encountered GM OBD1 codes:
- 12: System normal
- 13: Oxygen sensor circuit open
- 14: Coolant sensor high resistance or shorted
- 15: Coolant sensor circuit low or open
- 16: Direct ignition system (DIS) fault in circuit
- 17: Cam position sensor fault
- 18: Crank or cam sensor error
- 19: Crank sensor circuit fault
- 21: TPS sensor out of range
- 22: TPS sensor signal voltage low
- 23: Intake air temp sensor out of range, low
- 24: Vehicle speed (VSS) sensor circuit fault
- 25: Air temp sensor sensor out of range, high
- 26: Quad-driver module (computer) circuit #1 fault
- 27: Quad-driver module (computer) 2nd gear circuit
- 28: Quad-driver module (computer) circuit #2 fault
- 29: Quad driver module (computer) 4th gear circuit
- 31: Cam position sensor fault
- 32: EGR circuit fault
- 33: MAP sensor signal out of range, high
- 34: MAP sensor signal out of range, low
- 35: Idle air control sensor circuit fault
- 36: Ignition system circuit error
- 38: Brake input circuit fault
- 39: Clutch input circuit fault
- 41: Cam sensor circuit fault, ignition control circuit fault
- 42: Electronic spark timing (EST) circuit grounded
- 43: Knock sensor or electronic spark control circuit fault
- 44: Oxygen sensor lean exhaust
- 45: Oxygen sensor rich exhaust
- 46: Pass-key II circuit or PS.pressure switch circuit fault
- 47: PCM-BCM data circuit
- 48: Misfire diagnosis
- 51: Calibration error, MEM-CAL, ECM or EEPROM failure
- 52: Engine oil temperature circuit, low temperature indicated
- 53: Battery voltage error or EGR or Pass-key II circuit
- 54: EGR system failure or fuel pump circuit low voltage
- 55: A/D converter error or PCM not grounded or lean fuel or grounded reference voltage
- 56: Quad-driver module #2 circuit
- 57: Boost control problem
- 58: Vehicle anti-theft system fuel enable circuit
- 61: A/C system performance or degraded oxygen sensor signal
- 62: Engine oil temperature high temperature indicated
- 63: Oxygen sensor right side circuit open or MAP sensor out of range
- 64: Oxygen sensor right side lean exhaust indicated
- 65: Oxygen sensor right side rich exhaust indicated
- 66: A/C pressure sensor circuit low pressure
- 67: A/C pressure sensor circuit or A/C clutch circuit failure
- 68: A/C compressor relay circuit failure
- 69: A/C clutch circuit head pressure high
- 70: A/C refrigerant pressure circuit high
- 71: A/C evaporator temperature sensor circuit low
- 72: Gear selector switch circuit
- 73: A/C evaporator temperature circuit high
- 75: Digital EGR #1 solenoid error
- 76: Digital EGR #2 solenoid error
- 77: Digital EGR #3 solenoid error
- 79: Vehicle speed sensor (VSS) circuit signal high
- 80: Vehicle speed sensor (VSS) circuit signal low
- 81: Brake input circuit fault
- 82: Ignition control (IC) 3X signal error
- 85: PROM error
- 86: Analog/digital ECM error
- 87: EEPROM error
- 99: Power management
Important Considerations:
- Accuracy of Paper Clip Method: Be aware that the paper clip method for retrieving codes has mixed reviews regarding reliability and accuracy. Some users find it effective, while others experience inconsistencies.
- Professional Scan Tools: For a more reliable and comprehensive diagnostic approach, especially with a 16-pin connector, consider using an OBD2 scan tool. While your 1999 Chevy Monte Carlo might be OBD 1.5, many basic OBD2 scanners can still read some generic codes.
- Consult a Professional: If you are unsure about interpreting codes or performing diagnostic procedures, it’s always best to consult a qualified mechanic.
Conclusion
Determining the OBD2 pin count and understanding the diagnostic system of your 1999 Chevy Monte Carlo is the first step in addressing any potential engine issues. By counting the pins on your DLC and understanding the possibility of an OBD 1.5 system, you can choose the appropriate method for retrieving diagnostic codes, whether it’s the traditional paper clip method or utilizing an OBD2 scan tool. Remember to consult the specific repair manual for your 1999 Chevy Monte Carlo for the most accurate pinout diagrams and diagnostic procedures.
