This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II (Dodge Ram Cummins, Chevy GMC Duramax, Isuzu, Volvo, Vauxhall, VW, etc.). Although generic, specific repair steps may vary by make/model.
Photo of a PCM with the cover removed:
If your OBD II-equipped vehicle has stored a P0602 code, it means the Powertrain Control Module (PCM) has detected an internal programming error. The programming error applies to the PCM itself.
When you look at a PCM, you may only see a metal box, but what’s inside is crucial for effective engine operation. Essential information for engine management is factory-programmed using Electronically Erasable Programmable Read-Only Memory (EEPROM).
Vehicle-specific settings for engine and transmission management are programmed into the EEPROM for each vehicle leaving the factory. The EEPROM not only helps manage engine efficiency and performance but also serves to recognize and interact with other onboard vehicle control modules.
If the PCM detects inconsistencies with the EEPROM, or if it does not recognize the EEPROM program, a P0602 code will be stored and a Malfunction Indicator Lamp (MIL) may illuminate. Depending on the severity of the malfunction, several ignition cycles (with a malfunction) may be required for MIL illumination.
Other internal control module error codes include:
P0601 Internal Control Module Memory Checksum Error
P0603 Internal Control Module Keep Alive Memory (KAM) Error
P0604 Internal Control Module Random Access Memory (RAM) Error
P0605 Internal Control Module Read Only Memory (ROM) Error
Code Severity and Symptoms
A stored P0602 code should be classified as severe because the conditions that caused its storage can significantly affect engine management.
Symptoms of a P0602 code may include:
No-start condition
Multiple driveability issues
Harsh or erratic automatic transmission shifting
Reduced fuel economy
Engine may stall or idle roughly
Possible causes of this code include:
- PCM programming error
- New or incorrect PCM
- Aftermarket (high-performance) PCM program installed
- Blown ECM/PCM fuse
- Faulty ECM/PCM power relay
- Defective ECM/PCM
- Open or shorted wiring or connectors in the CAN harness
- Unsecured control module ground strap or broken ground wire
Diagnostic and Repair Procedures
Diagnosing a P0602 code can be challenging, even for the most experienced and well-equipped technician. Nevertheless, there are some preliminary tests that can be performed before throwing up your hands and passing the problem to someone else.
As usual, I would start my diagnosis with a visual inspection of the engine management wiring harnesses and connectors. Any damaged or burnt wiring and connectors should be repaired or replaced. Next, I would connect the scanner to the vehicle’s diagnostic connector and retrieve all stored codes and freeze frame data. Before clearing the codes, I would note them down in case it turns out to be an intermittent code. A P0602 code must be diagnosed and repaired before diagnosing and repairing any other stored codes, as other stored codes are likely false. Now clear the codes in the hope that the P0602 was stored in error.
If the P0602 immediately resets, check the battery voltage at the PCM. The PCM requires battery voltage to operate correctly. If the battery terminals are corroded or loose, inadequate voltage may reach the PCM. Check the PCM relays and fuses for battery voltage with the circuit loaded. Corroded fuses may look normal until a load is applied to the circuit and their fault is revealed.
Obviously, if the PCM has been recently replaced, the likelihood of it being incorrectly programmed or not programmed at all is high. Additionally, a controller from another vehicle can only be used if it has been reprogrammed specifically for the vehicle in question, and aftermarket (high-performance) programmers may not be recognized by other controllers (especially initially), resulting in the storage of a P0602.
Incorrectly programmed or replaced controllers can be reprogrammed with a factory scanner. If you cannot access such a scanner, most dealerships offer PCM programming for a modest fee. Some aftermarket PCM manufacturers offer pre-programmed controllers for certain models. Check with your auto parts supplier and have the vehicle identification number, mileage, and other relevant data available.
Additional Diagnostic Notes:
New or used, a replacement PCM will need to be programmed to match the vehicle in question
Aftermarket or high-performance programmers will often need time for other controllers to recognize them – if they do at all