The Chrysler PT Cruiser, a vehicle known for its unique retro styling, can sometimes present modern automotive challenges, particularly within its onboard diagnostic (OBDII) system. While the original case study detailed a 2006 model, understanding OBDII diagnostics remains highly relevant for earlier models like the 2002 PT Cruiser. This write-up delves into a real-world scenario of troubleshooting OBDII communication and transmission problems, offering insights valuable for anyone facing similar issues with their 2002 Pt Cruiser Obdii system.
Initial Encounter and Symptoms
The subject vehicle, a 2006 PT Cruiser (note: while the case is on a 2006 model, the diagnostic principles are broadly applicable to the 2002 PT Cruiser OBDII system), had been sitting idle for approximately ten days. Initial attempts to start the vehicle revealed a weak battery, a common issue with cars left unused. After a couple of hours on a charger, the engine cranked to life. However, the check engine light (CEL) and anti-lock braking system (ABS) lights remained illuminated, indicating underlying problems within the vehicle’s systems.
Prior to this diagnostic session, attempts to communicate with the car’s computer using an OBDII scanner had failed entirely. This “no communication” scenario, often pointing to a problem with the Controller Area Network (CAN) bus, was further complicated by the vehicle being stuck in limp-in mode, limiting the transmission to second gear.
Unexpected Turnaround and Initial OBDII Scan
Surprisingly, upon driving the PT Cruiser after charging the battery, the transmission began shifting normally. All four gears engaged smoothly, and the gear selector (PRNDL) displayed the correct gear. This unexpected improvement suggested that the initial issue might have been related to low voltage or temporary electrical glitches.
Capitalizing on this window of opportunity, and before switching off the engine, an OBDII scanner was connected. This time, unlike previous attempts, the scanner successfully established communication with the CAN system and retrieved a series of diagnostic trouble codes (DTCs). These codes offered the first concrete clues in pinpointing the root cause of the problems with the 2002 PT Cruiser OBDII system, even though this specific scan was on a slightly later model year.
Decoding the Fault Codes
The initial OBDII scan revealed a multitude of stored codes, highlighting issues across various vehicle systems. It’s important to note that some codes might be historical, accumulated over time, and not necessarily indicative of the current problem. The codes were categorized as follows:
OBD II (7 codes stored):
- P1603 – PCM Internal dual port RAM communications failure: This code suggests a problem within the Powertrain Control Module (PCM) itself, specifically with its internal communication processes.
- P0700 – TCS (MIL Request) /Malfunction Indicator Light/: This is a generic transmission system fault code, indicating that the Transmission Control System (TCS) has requested the Malfunction Indicator Light (MIL), or check engine light, to illuminate.
- U0101 – Lost Communications w/TCM: This communication fault code points to a loss of communication between the PCM and the Transmission Control Module (TCM).
- P0562 – Battery Low: This code confirms the earlier suspicion of a low battery voltage condition.
- P0700 – TCS (MIL Request) /Malfunction Indicator Light/: (Duplicate code)
- U0101 – Lost Communications w/TCM: (Duplicate code)
- P1603 – PCM Internal dual port RAM communications failure: (Duplicate code)
SRS (Supplemental Restraint System):
- U1415 – Implausible data: This code indicates that the SRS module has received data that is not plausible or valid.
- U1414 – Implausible ECU Network Configuration Data: This suggests a configuration issue within the ECU network, potentially affecting communication between modules.
ABS (Anti-lock Braking System):
- C100A – LF Speed Sensor Circuit: This code points to a problem with the circuit for the left front (LF) wheel speed sensor.
- U140E – Implausible Data: Similar to the SRS code, this indicates implausible data received by the ABS module.
- C2202 – VIN Mismatch: This code suggests a mismatch between the Vehicle Identification Number (VIN) stored in the ABS module and the vehicle’s actual VIN, potentially indicating a module replacement or programming issue.
- C2100 – Battery Disconnected: This code again points to a past or present battery disconnection event.
- C101F – RF Speed Sensor: This code indicates a problem with the right front (RF) wheel speed sensor circuit.
- U0141 Lost communication w/Instrument Panel Module (FCM/TIPM) /front control module/total integrated power module/: This communication fault suggests a loss of communication with the Instrument Panel Module, which is often integrated into the Front Control Module (FCM) or Total Integrated Power Module (TIPM).
- U0002 – Can C Bus Off Performance: This code directly indicates a performance issue with the CAN C bus, the communication network within the vehicle.
Chrysler Specific Codes:
- P0700 – TCS (MIL Request) /Malfunction Indicator Light/: (Duplicate code)
- U0101 – Lost Communications w/TCM: (Duplicate code)
- P1684 – Battery Disconnected: (Duplicate code, Chrysler specific)
- P0952 – Autostick Input Circuit Low: This code relates to a low input signal from the Autostick system (if equipped).
- P0613 – Internal Transmission Processor: This code points to a potential fault within the internal processor of the transmission control system.
- P0562 – Battery Low: (Duplicate code, Chrysler specific)
Initial Deductions and Code Clearing
Based on the retrieved codes, several potential issues emerged. The battery-related codes (P0562, P1684, C2100) were likely secondary, resulting from the vehicle sitting idle. However, a weak battery can indeed trigger a cascade of seemingly unrelated codes.
The VIN mismatch code (C2202) and implausible data faults (U1414, U1415, U140E) initially raised suspicion of a potential ECU swap without proper programming. However, after clearing all DTCs and restarting the vehicle, these specific codes did not immediately reappear. This suggested they might have been historical anomalies.
Crucially, the communication fault codes (U0101, U0141, U0002, P1603) and the wheel speed sensor codes (C100A, C101F) remained significant. The persistent P1603 (PCM Internal dual port RAM communications failure) was particularly concerning, suggesting a deeper internal PCM issue or related wiring problems.
Recurrence of Limp-in Mode and Persistent Codes
After clearing all codes and taking the PT Cruiser for another test drive, the transmission reverted back to limp-in mode. A subsequent OBDII scan revealed a significantly reduced set of stored codes:
- C100A – LF Speed Sensor Circuit
- U0101 – Lost Communications w/TCM
- P1603 – PCM Internal dual port RAM communications failure
This narrowed down the immediate problem to these three persistent codes. The reappearance of C100A strongly indicated a genuine issue with the left front wheel speed sensor circuit. The U0101 and P1603 codes further reinforced the suspicion of communication problems, possibly intertwined with the wheel speed sensor issue or related to the PCM itself.
Next Steps in Diagnosis: Focusing on Persistent Faults
The diagnostic process led to several key conclusions:
- Transmission Functionality: The transmission itself appeared mechanically sound, as evidenced by its proper shifting after the initial battery charge. The problem seemed to be electrical or electronic control related.
- Wheel Speed Sensor: The consistent C100A code pointed directly to the left front ABS wheel speed sensor circuit as a prime suspect. This could involve the sensor itself, its wiring, or connections.
- Communication Issues (CAN Bus/PCM/TCM): The persistent U0101 and P1603 codes indicated ongoing communication problems. P1603, in particular, suggested potential issues with PCM wiring (grounds, power supply, fuses, relays), or even a faulty PCM itself.
Further investigation would need to focus on:
- Verifying the Left Front Wheel Speed Sensor Circuit: Testing the sensor, wiring continuity, and connections.
- Examining PCM and TCM Wiring and Connections: Checking for any signs of damage, corrosion, or loose connections, particularly grounds and power supplies.
- Considering PCM/TCM Issues: While less common, a faulty PCM or TCM could not be ruled out, especially given the P1603 code. Programming issues were also a possibility, although less likely after clearing initial VIN mismatch codes.
Seeking Expert Advice
The troubleshooter in the original scenario rightly sought advice at this stage, acknowledging the complexity of the problem and the need for further expertise. Troubleshooting complex OBDII and communication issues often requires a systematic approach, specialized tools (like oscilloscopes for CAN bus diagnosis), and in-depth knowledge of the specific vehicle’s electrical and control systems. For owners of a 2002 PT Cruiser OBDII system facing similar challenges, a methodical approach, starting with the persistent fault codes and systematically eliminating potential causes, is crucial for effective diagnosis and repair.
