Error Code P0602 is defined as Control Module Programming Error. This means there’s a programming error in one of the control modules, which includes engine problems like rough idling, engine stalling, and poor acceleration.

This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, especially those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs of course, vary from one make and/or model to another.


If the vehicle stores this code that means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected an internal programming error, which applies to the PCM itself.

When Error Code P0602 is set, it usually refers to a programming error in one of the vehicle’s control module, which includes the body control module, transmission control module, antilock brake control module, anti-theft module, cruise control module, climate control module, fuel injection control module, proximity alert module, instrument panel control module, traction control module and turbo control module.

Other related internal control module error codes include:

Mechanics should also remember that some vehicles may require multiple drive cycles, upwards of eight, before the Check Engine light is triggered on the dashboard. The PCM however, will still store the code the first time the error appears.

Common Symptoms

Error Code P0602 can be categorized as a serious problem, because the conditions that caused it to be stored will definitely affect engine management in major ways. With this, symptoms include:

  • Hard or no start condition
  • Decreased fuel efficiency
  • Engine stalling or rough idling
  • Harsh or erratic shifting in transmission

Possible Causes

Poor electrical connection, programming error, or defective PCM driver are the three most likely causes for Error Code P0602. Other possible causes include:

  • Faulty, corroded or damaged connectors or wirings within CAN (Control Area Network) Bus harness
  • Broken ground wire, or loose module ground strap
  • Defective CAN bus
  • New or wrong PCM
  • Installed aftermarket (high-performance) PCM program
  • Blown PCM fuse
  • Bad PCM power supply relay
  • Open or shorted wiring or connectors in CAN harness

How to Check

As with many error codes, diagnosing P0602 requires the use of OBD-II scanner and DVOM (digital volt/ohmmeter).

  • First, technicians will check all connectors, wirings and components and look for any signs of damage or loose connections
  • Then, they will download freeze frame data and any trouble codes stored. This information is important when trying to determine the order in which the codes were set.
  • Next, they will clear the codes and take the vehicle for a test drive to see if the code returns.
  • If the code returns, technicians will use a specialized scanner, such as Tech 2 or Autohex, to determine the cause of the stored code quickly. Otherwise, diagnosis can be time-consuming.
  • Then, the mechanic will test any circuitry while the vehicle is in operation to get best results.
  • The technician will then install some sort of memory saving device. If failed to do so, he will have to reprogram the PCM and other control modules should a probe is misplaced.
  • Next, the mechanic will test for continuity and ground with the battery in all control modules associated using the DVOM and auxiliary ground cable.
  • Next, the mechanic will test the continuity between individual control modules using CAN Bus system wiring diagram.
  • Lastly, they will clear the codes and retest the system again and see if the code returns.

How to Fix

After a thorough diagnosis, the technicians will be able to come up with the right repair route for the error code, which usually include:

  • Replacing damaged or faulty connectors, components or wirings, and make sure all connectors are secured
  • Replacing of faulty components in individual control modules
  • Replacing faulty PCM

The most common misdiagnosis for this error code is mistaking it with codes relating to engine misfire, lean exhaust or fuel injector, which would obviously lead to misdiagnosis and unsuccessful repair.

Aside from the decrease in vehicle performance characterized by poor acceleration, shifting and idling, Error Code P0602 can definitely affect fuel mileage, making the vehicle less fuel efficient.