Navigating the intricacies of vehicle diagnostics can be daunting, especially when dealing with classic cars like the 1994 Buick Roadmaster. Understanding the On-Board Diagnostics II (OBD2) system is crucial for identifying and resolving issues, ensuring your Roadmaster runs smoothly. This comprehensive guide breaks down the diagnostic trouble codes specific to your 1994 Buick Roadmaster, empowering you with the knowledge to understand your vehicle’s health.
Decoding PCM Diagnostic Codes (-00)
The Powertrain Control Module (PCM) is the brain of your Buick Roadmaster’s engine management system. These codes relate to engine and transmission issues.
- Code 11: Malfunction Indicator Lamp (MIL) Circuit: This indicates a problem with the circuit that controls the check engine light.
- Code 13: Bank 1 (Left) Heated O2 Sensor (Open Circuit): Signifies an open circuit in the heated oxygen sensor on bank 1, which can affect fuel efficiency and emissions.
- Code 14: Engine Coolant Temperature Sensor (Signal Voltage Low, High Temperature Indicated): Indicates the engine coolant temperature sensor is reporting a high temperature, possibly due to low coolant or sensor malfunction.
- Code 15: Engine Coolant Temperature Sensor (Signal Voltage High, Low Temperature Indicated): Signals the engine coolant temperature sensor is reporting a low temperature, which could be a sensor issue or a wiring problem.
- Code 16: Distributor Ignition System (Low Resolution Pulse): Points to a problem with the low-resolution pulse signal from the distributor ignition system, which can affect timing and engine performance.
- Code 18: Injector Circuits: Indicates a general issue within the injector circuits, potentially affecting fuel delivery to one or more cylinders.
- Code 21: Throttle Position Sensor (TPS) Circuit (Signal Voltage High): Suggests the TPS is sending a high voltage signal, possibly indicating a sensor malfunction or wiring issue.
- Code 22: Throttle Position Sensor (TPS) Circuit (Signal Voltage Low): Indicates the TPS is sending a low voltage signal, potentially due to a sensor malfunction or wiring problem.
- Code 23: Air Intake Temperature (IAT) Sensor Circuit (Signal Voltage High, Low Temperature Indicated): Signals the IAT sensor is reporting a low temperature, which could be a sensor problem or wiring issue.
- Code 24: Vehicle Speed Sensor (VSS) Circuit: Indicates a problem with the VSS circuit, affecting speedometer readings and potentially transmission shifting.
- Code 25: Air Intake Temperature (IAT) Sensor Circuit (Signal Voltage Low, High Temperature Indicated): Suggests the IAT sensor is reporting a high temperature, potentially due to a sensor issue or wiring problem.
- Code 26: Evaporative Emission (EVAP) Canister Purge Solenoid Circuit: Indicates a fault in the EVAP canister purge solenoid circuit, affecting the emission control system.
- Code 27: Exhaust Gas Recirculation (EGR) Vacuum Control Signal Solenoid Valve Circuit: Signals a problem with the EGR vacuum control solenoid circuit, impacting emission control and potentially engine performance.
- Code 28: Transmission Range (TR) Pressure Switch Assembly Fault: Indicates a fault within the transmission range pressure switch assembly, which can affect gear selection and transmission operation.
- Code 29: Secondary Air Injector (AIR) Pump Circuit: Points to an issue with the secondary air injection pump circuit, related to emission control during cold starts.
- Code 32: Exhaust Gas Recirculation (EGR) Fault (1 of 2): Indicates a general EGR system fault, potentially affecting emissions and engine performance.
- Code 33: Manifold Absolute Pressure (MAP) Sensor Circuit (Signal Voltage High – Vacuum Low): Suggests the MAP sensor is reporting a low vacuum/high pressure, possibly due to a sensor or vacuum leak issue.
- Code 34: Manifold Absolute Pressure (MAP) Sensor Circuit (Signal Voltage Low – Vacuum High): Indicates the MAP sensor is reporting a high vacuum/low pressure, potentially due to a sensor malfunction or vacuum line issue.
- Code 36: Distributor Ignition System (Faulty High Resolution Pulse or Extra Low Resolution Pulse Detected): Signals a problem with the high-resolution pulse from the distributor, which is critical for accurate ignition timing.
- Code 37: Brake Switch Stuck On: Indicates the brake switch is stuck in the ‘on’ position, which can affect cruise control and potentially other systems.
- Code 38: Brake Switch Stuck Off: Indicates the brake switch is stuck in the ‘off’ position, which can affect brake light operation and other systems.
- Code 41: Ignition Control (IC) Circuit (Open): Points to an open circuit in the ignition control circuit, which can prevent spark and cause engine misfires.
- Code 42: Ignition Control (IC) Circuit (Shorted or Grounded Circuit): Suggests a short or grounded circuit in the ignition control system, potentially causing ignition problems.
- Code 43: Knock Sensor (KS) Circuit: Indicates a fault in the knock sensor circuit, which is used to detect engine knocking and adjust timing.
- Code 44: Bank 1 (Left) Heated O2 Sensor Circuit (Lean Exhaust Indicated): Signals a lean exhaust condition detected by the O2 sensor on bank 1, potentially indicating a fuel delivery issue or vacuum leak.
- Code 45: Bank 1 (Left) Heated O2 Sensor Circuit (Rich Exhaust Indicated): Indicates a rich exhaust condition detected by the O2 sensor on bank 1, possibly due to overfueling or an issue with the sensor.
- Code 46: PASS-Key II Circuit: Relates to the PASS-Key II anti-theft system circuit, potentially indicating a problem with key recognition or system malfunction.
- Code 47: Knock Sensor Circuit or Control Module Missing: Suggests a missing knock sensor or a fault in the knock sensor control module.
- Code 48: Mass Air Flow (MAF) Sensor Circuit: Indicates a problem with the MAF sensor circuit, which measures the amount of air entering the engine and is crucial for fuel mixture calculation.
- Code 50: System Voltage Low: Signals a low system voltage condition, which can affect various electronic components.
- Code 51: EEPROM Programming Error: Indicates an error in the Electrically Erasable Programmable Read-Only Memory (EEPROM) programming within the PCM.
- Code 53: System Voltage High: Signals a high system voltage condition, which can damage electronic components.
- Code 55: Fuel Lean Monitor: Indicates the system has detected a consistently lean fuel condition.
- Code 58: Transmission Fluid Temp (TFT) Sensor Circuit Low (High Temperature Indicated): Suggests the TFT sensor is reporting a high temperature, possibly due to overheating or sensor malfunction.
- Code 59: Transmission Fluid Temp (TFT) Sensor Circuit High (Low Temperature Indicated): Indicates the TFT sensor is reporting a low temperature, which could be a sensor issue or wiring problem.
- Code 63: Bank 2 (Right) Heated Oxygen Sensor (HO2S) Circuit (Open Circuit): Signifies an open circuit in the heated oxygen sensor on bank 2.
- Code 64: Bank 2 (Right) Heated Oxygen Sensor (HO2S) Circuit (Lean Exhaust Indicated): Signals a lean exhaust condition detected by the O2 sensor on bank 2.
- Code 65: Bank 2 (Right) Heated Oxygen Sensor (HO2S) Circuit (Rich Exhaust Indicated): Indicates a rich exhaust condition detected by the O2 sensor on bank 2.
- Code 66: A/C Pressure Refrigerant Circuit (Open or Shorted): Indicates an open or shorted circuit in the A/C pressure refrigerant circuit, affecting the air conditioning system.
- Code 67: A/C Pressure Refrigerant Circuit (Pressure Sensor or A/C Clutch Circuit Problem): Signals a problem with the A/C pressure sensor or the A/C clutch circuit.
- Code 68: A/C Relay Circuit (Shorted Circuit): Indicates a shorted circuit in the A/C relay circuit.
- Code 69: A/C Clutch Circuit: Points to a general issue within the A/C clutch circuit.
- Code 70: A/C Clutch Relay Driver Circuit: Indicates a problem with the A/C clutch relay driver circuit.
- Code 72: Vehicle Speed Sensor Loss: Signals a loss of signal from the vehicle speed sensor.
- Code 73: Pressure Control Solenoid (PCS) Circuit (Current Error): Indicates a current error in the pressure control solenoid circuit within the transmission.
- Code 74: Traction Control System (TCS) Circuit Low: Signals a low voltage condition in the traction control system circuit.
- Code 75: Transmission System Voltage Low: Indicates a low voltage condition specifically within the transmission system.
- Code 77: Primary Cooling Fan Relay Control Circuit (Not Used with V08 Option): Relates to the primary cooling fan relay circuit, but may not be applicable depending on vehicle options (V08).
- Code 78: Secondary Cooling Fan Relay Control Circuit: Indicates a problem with the secondary cooling fan relay control circuit.
- Code 79: Transmission Fluid Overtemp: Signals that the transmission fluid temperature is too high.
- Code 81: Transmission 2-3 Shift Solenoid Circuit: Indicates a problem with the 2-3 shift solenoid circuit within the transmission.
- Code 82: Transmission 1-2 Shift Solenoid Circuit: Indicates a problem with the 1-2 shift solenoid circuit within the transmission.
- Code 84: Transmission 3-2 Control Solenoid Circuit: Indicates a problem with the 3-2 control solenoid circuit within the transmission.
- Code 85: Transmission TCC Stuck “ON”: Signals that the Transmission Torque Converter Clutch (TCC) is stuck in the ‘on’ position.
- Code 90: Transmission TCC Solenoid Circuit: Indicates a problem with the TCC solenoid circuit.
- Code 95: Change Oil Lamp Circuit: Indicates a problem with the circuit controlling the “Change Oil” lamp.
- Code 96: Low Oil Lamp Circuit: Indicates a problem with the circuit controlling the “Low Oil” lamp.
- Code 97: VSS Output Circuit: Signals a problem with the output circuit of the Vehicle Speed Sensor.
Understanding CCM Diagnostic Trouble Codes (-01)
The Central Control Module (CCM) manages various convenience and body electrical functions in your 1994 Buick Roadmaster.
- Code 20: RAP Enable Circuit (Circuit Shorted to Battery): Indicates a short to battery in the Retained Accessory Power (RAP) enable circuit.
- Code 21: RAP Enable Circuit (Circuit Open or Shorted to Ground): Signals an open or short to ground in the RAP enable circuit.
- Code 22: DIL Enable Circuit (Circuit Shorted to Battery): Indicates a short to battery in the Driver Information Loop (DIL) enable circuit.
- Code 23: DIL Enable Circuit (Circuit Open or Shorted to Ground): Signals an open or short to ground in the DIL enable circuit.
- Code 24: Courtesy Output Circuit (Circuit Shorted to Battery): Indicates a short to battery in the courtesy light output circuit.
- Code 25: Courtesy Output Circuit (Circuit Open or Shorted to Ground): Signals an open or short to ground in the courtesy light output circuit.
- Code 26: VES Output Circuit (Circuit Open or Shorted to Ground): Signals an open or short to ground in the Vehicle Entry System (VES) output circuit.
- Code 27: VES Output Circuit (Circuit Shorted to Battery): Indicates a short to battery in the VES output circuit.
- Code 28: VES Tracking Error (Circuit Open, Shorted to Ground, or Shorted to Battery): Signals a VES tracking error, potentially due to circuit issues.
- Code 30: “PASS KEY FAULT” Telltale Circuit (Circuit Shorted to Battery): Indicates a short to battery in the “PASS KEY FAULT” indicator circuit.
- Code 31: “PASS KEY FAULT” Telltale Circuit (Circuit Open or Shorted to Ground): Signals an open or short to ground in the “PASS KEY FAULT” indicator circuit.
- Code 32: Fuel Enable Circuit (Circuit Shorted to Battery): Indicates a short to battery in the fuel enable circuit.
- Code 33: Fuel Enable Circuit (Circuit Open or Shorted to Ground): Signals an open or short to ground in the fuel enable circuit.
- Code 34: Headlamp Enable Circuit (Circuit Shorted to Battery): Indicates a short to battery in the headlamp enable circuit.
- Code 35: Park Lamp Enable Circuit (Circuit Shorted to Battery): Indicates a short to battery in the park lamp enable circuit.
- Code 36: DRL Enable Circuit (Circuit Shorted to Battery): Indicates a short to battery in the Daytime Running Lights (DRL) enable circuit.
- Code 37: DRL Enable Circuit (Circuit Open or Shorted to Ground): Signals an open or short to ground in the DRL enable circuit.
- Code 38: EEPROM Calibration Error: Indicates an error in the EEPROM calibration within the CCM.
- Code 39: EEPROM Calibration ID Error: Indicates an error with the EEPROM calibration identification.
- Code 40: Delay Pot Circuit (Circuit Shorted to Ground): Indicates a short to ground in the delay potentiometer circuit.
- Code 41: Delay Pot Circuit (Circuit Open or Shorted to Battery): Signals an open or short to battery in the delay potentiometer circuit.
- Code 42: Key Resistor Circuit (Circuit Shorted to Ground): Indicates a short to ground in the key resistor circuit.
- Code 43: Key Resistor Circuit (Circuit Open or Shorted to Battery): Signals an open or short to battery in the key resistor circuit.
- Code 44: Steering Wheel Sensor Circuit (Circuit Open or Shorted to Ground): Signals an open or short to ground in the steering wheel sensor circuit.
- Code 45: Steering Wheel Sensor Circuit (Circuit Open or Shorted to Battery): Signals an open or short to battery in the steering wheel sensor circuit.
- Code 46: CCM Internal Failure: Indicates an internal failure within the Central Control Module itself.
- Code 47: Canadian Select Input Error: Indicates an error with the Canadian select input, possibly related to regional vehicle configurations.
HVAC Diagnostic Trouble Codes (-02)
These codes are related to the Heating, Ventilation, and Air Conditioning (HVAC) system of your 1994 Buick Roadmaster.
- Code 01: Outside Air Temperature Sensor Circuit (Circuit Open): Indicates an open circuit in the outside air temperature sensor circuit.
- Code 02: Outside Air Temperature Sensor Circuit (Circuit Shorted): Indicates a shorted circuit in the outside air temperature sensor circuit.
- Code 03: In-Car Air Temperature Sensor Circuit (Circuit Open): Indicates an open circuit in the in-car air temperature sensor circuit.
- Code 04: In-Car Air Temperature Sensor Circuit (Circuit Shorted): Indicates a shorted circuit in the in-car air temperature sensor circuit.
- Code 05: Sun Load Sensor Circuit (Circuit Open): Indicates an open circuit in the sun load sensor circuit.
- Code 06: Sun Load Sensor Circuit (Circuit Shorted): Indicates a shorted circuit in the sun load sensor circuit.
- Code 10: Air Mix Motor Circuit (Circuit Open): Indicates an open circuit in the air mix motor circuit.
- Code 11: Air Mix Motor Circuit (Circuit Shorted): Indicates a shorted circuit in the air mix motor circuit.
- Code 26: Serial Data Communication (Circuit Shorted to Battery, Shorted to Ground, or Circuit Open): Indicates a problem with serial data communication, potentially a short or open circuit.
- Code 27: Invalid EEPROM Detected: Indicates an invalid EEPROM detected within the HVAC control module.
SIR Diagnostic Trouble Codes (-03)
The Supplemental Inflatable Restraint (SIR) system, or airbags, is crucial for safety. These codes pertain to the airbag system in your 1994 Buick Roadmaster.
- Code 15: Passenger Deployment Loop Resistance High: Indicates high resistance in the passenger airbag deployment loop.
- Code 16: Passenger Deployment Loop Resistance Low: Indicates low resistance in the passenger airbag deployment loop.
- Code 17: Passenger Deployment Loop Open: Indicates an open circuit in the passenger airbag deployment loop.
- Code 21: Driver Deployment Loop Resistance High: Indicates high resistance in the driver airbag deployment loop.
- Code 22: Driver Deployment Loop Resistance Low: Indicates low resistance in the driver airbag deployment loop.
- Code 24: Deployment Loop Voltage Low: Indicates low voltage in the airbag deployment loop.
- Code 25: Deployment Loop Shorted to Ignition: Indicates a short to ignition in the airbag deployment loop.
- Code 26: Driver’s Deployment Loop Open: Indicates an open circuit in the driver airbag deployment loop.
- Code 35: ADS (Auxiliary Discriminating Sensor) Missing/Shorted to Ground: Indicates a missing or shorted Auxiliary Discriminating Sensor (ADS).
- Code 36: ADS Closed/Shorted to Voltage: Indicates a closed or shorted to voltage condition in the ADS.
- Code 51: Frontal Crash Detected: Indicates a frontal crash has been detected by the SIR system.
- Code 52: Crash Data Area Full: Indicates the crash data memory area is full.
- Code 61: Lamp Circuit Failure: Indicates a failure in the SIR warning lamp circuit.
- Code 62: Redundant Lamp Circuit Failure: Indicates a failure in the redundant SIR warning lamp circuit.
- Code 71: Internal SDM Malfunction: Indicates an internal malfunction within the Sensing and Diagnostic Module (SDM).
ABS/TC Diagnostic Trouble Codes (-04)
These codes relate to the Anti-lock Braking System (ABS) and Traction Control (TC) system in your 1994 Buick Roadmaster.
- Code 21: RF Wheel Speed Sensor Circuit Malfunction: Indicates a malfunction in the right front wheel speed sensor circuit.
- Code 23: RF Wheel Speed Sensor Circuit Continuity Malfunction: Indicates a continuity malfunction in the right front wheel speed sensor circuit.
- Code 25: LF Wheel Speed Sensor Circuit Malfunction: Indicates a malfunction in the left front wheel speed sensor circuit.
- Code 27: LF Wheel Speed Sensor Circuit Continuity Malfunction: Indicates a continuity malfunction in the left front wheel speed sensor circuit.
- Code 28: Wheel Speed Sensor Circuit Frequency Malfunction: Indicates a frequency malfunction in a wheel speed sensor circuit.
- Code 31: RR Wheel Speed Sensor Circuit Malfunction: Indicates a malfunction in the right rear wheel speed sensor circuit.
- Code 33: RR Wheel Speed Sensor Circuit Continuity Malfunction: Indicates a continuity malfunction in the right rear wheel speed sensor circuit.
- Code 35: LR Wheel Speed Sensor Circuit Malfunction: Indicates a malfunction in the left rear wheel speed sensor circuit.
- Code 37: LR Wheel Speed Sensor Circuit Continuity Malfunction: Indicates a continuity malfunction in the left rear wheel speed sensor circuit.
- Code 41: Right Front Valve Solenoid Malfunction: Indicates a malfunction in the right front ABS valve solenoid.
- Code 42: RH Outlet Valve Solenoid Malfunction: Indicates a malfunction in the right rear outlet valve solenoid.
- Code 45: Left Front Valve Solenoid Malfunction: Indicates a malfunction in the left front ABS valve solenoid.
- Code 46: LF Outlet Valve Solenoid Malfunction: Indicates a malfunction in the left front outlet valve solenoid.
- Code 47: ASV Prime Line Solenoid Malfunction: Indicates a malfunction in the ASV (possibly Anti-lock System Valve) prime line solenoid.
- Code 48: USV Pilot Valve Solenoid Malfunction: Indicates a malfunction in the USV (possibly Upstream Valve) pilot valve solenoid.
- Code 51: Right Rear Valve Solenoid Malfunction: Indicates a malfunction in the right rear ABS valve solenoid.
- Code 52: RR Outlet Valve Solenoid Malfunction: Indicates a malfunction in the right rear outlet valve solenoid.
- Code 55: Left Rear Valve Solenoid Malfunction: Indicates a malfunction in the left rear ABS valve solenoid.
- Code 56: LR Outlet Valve Solenoid Malfunction: Indicates a malfunction in the left rear outlet valve solenoid.
- Code 57: TCC Disable Relay Output Malfunction: Indicates a malfunction in the Torque Converter Clutch (TCC) disable relay output, related to traction control interaction with the transmission.
- Code 58: EBTCM Internal Adjuster Assembly Malfunction: Indicates an internal malfunction in the Electronic Brake and Traction Control Module (EBTCM) adjuster assembly.
- Code 61: Pump Motor or Pump Motor Relay Malfunction: Indicates a malfunction in the ABS pump motor or pump motor relay.
- Code 62: Traction Disable Switch Used or RPM Signal Malfunction: Indicates the traction disable switch has been used or there is an RPM signal malfunction.
- Code 63: Valve Solenoid Relay Malfunction: Indicates a malfunction in the ABS valve solenoid relay.
- Code 64: Throttle Position Signal Malfunction: Indicates a malfunction in the throttle position signal as it relates to the ABS/TC system.
- Code 65: Adjuster Assembly Circuit Malfunction: Indicates a malfunction in the adjuster assembly circuit within the EBTCM.
- Code 66: Adjuster Assembly Control Malfunction: Indicates a control malfunction within the EBTCM adjuster assembly.
- Code 67: Throttle Position Sensor Comparison Malfunction: Indicates a comparison malfunction between throttle position sensors, likely for ABS/TC control.
- Code 71: EBTCM Internal Malfunction: Indicates a general internal malfunction of the EBTCM.
- Code 72: Serial Data Link Malfunction: Indicates a malfunction in the serial data link communication to the EBTCM.
- Code 73: Spark Retard Monitoring Malfunction: Indicates a malfunction in the spark retard monitoring function of the ABS/TC system.
- Code 85: Low Voltage: Indicates a low voltage condition affecting the ABS/TC system.
This detailed breakdown of OBD2 trouble codes for your 1994 Buick Roadmaster should provide a solid foundation for diagnosing and addressing potential issues. Remember, while this guide is comprehensive, professional diagnosis and repair are always recommended for complex problems. Use this information to better understand your vehicle and communicate effectively with your mechanic, ensuring your classic Roadmaster stays on the road for years to come.
