Error Code P065D is defined as Reductant System Malfunction Lamp Control Circuit. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, particularly those made since 1996 up to present. This includes models from, but not limited to Audi, Chevrolet, Chrysler, Dodge, Ford, GMC, Ram, Volkswagen, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from make, model, and powertrain configuration.

Error Code P065D means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes), or one of the related controllers, has determined a discrepancy in the generator control circuit.

The reductant system malfunction lamp plays an important part in the instrumental panel. It’s designed to warn the driver for a possible fault in the reductant system. Usually, the PCM gets a signal from one of the sensors in the reductant system. These sensors allow the PCM to monitor any possible malfunctions in the system. When the PCM calculates the data from the reductant system, and a problem is detected, the PCM will emit a voltage signal to the reductant system malfunction warning lamp through the lamp control circuit. When the reductant system malfunction control lamp circuit is activated, the reductant system malfunction lamp should illuminate.

During KOEO (key on engine off) position, the vehicle starts a self-test for all instrument panel warning lamps. If a problem in monitoring the reductant system malfunction lamp control circuit has been detected, then Error Code P065D will be stored, and activate the Check Engine light.

Common Symptoms

  • Inoperable reductant system
  • Inoperable reductant system malfunction lamp
  • Reductant system malfunction lamp remains activated
  • Engine drivability issues
  • Catalytic converter-related error codes

Possible Causes

  • Defective reductant system malfunction bulb
  • Open or shorted circuit between the PCM and instrument panel or other controllers
  • A programming error in PCM
  • Defective PCM or other controllers

How to Check

If there are other reductant system codes present, then these should be addressed and repaired first before attempting to diagnose Error Code P065D.

As with most codes, the best way to start the diagnosis for this code is to check with the TSB (Technical Service Bulletins) and replicate the codes stored. Look for the same symptoms of the same year, make, model, and engine. Finding the right TSB usually leads to helpful diagnostic information.

Diagnostic scanner and DVOM (digital volt/ohmmeter) will also be necessary for more accurate diagnosis.

Start the diagnosis by connecting the scanner to the vehicle’s diagnostic port. Retrieve all stored codes and freeze frame data. You will want to take note of the code just in case they’re proven to be intermittent.

After recording all pertinent information, clear the codes and then take the vehicle for a test drive (if applicable) and see if the code resets, or the PCM enters readiness mode.

If the PCM enters readiness mode, that means the problem is intermittent. You may have to wait for the problem to worsen before you can accurately diagnose it. If the code does NOT reset, however, and there are no drivability symptoms, you can run the vehicle normally.

On the other hand, if the code resets, then you can proceed for a thorough inspection of the system and all its related wirings and connectors. Broken or unplugged harnesses must be repaired or replaced, as necessary.

If the connectors and wirings look functional, then use the vehicle information to obtain the right wiring diagram, connector pin-out charts, connector face views, and diagnostic flow charts. Once you have the right information, use the DVOM to test the reductant system malfunction lamp control circuit at the right pin of the PCM connector. If there are output signal detected in the reductant system malfunction lamp control, then you can suspect a defective or programming error in the PCM.

If the PCM discovers the reductant system malfunction lamp control output signal, then test the corresponding circuit (as it’s presented) at the reductant system malfunction lamp control circuit pin of the instrument panel connector. If there is no signal discovered, then you can suspect an open circuit between the PCM and the reductant system malfunction lamp in the instrument panel. Repair or replace the circuit as necessary, and then retest the system.

  • If the reductant system malfunction lamp is unable to activate during key on and engine off, then you can suspect a failure in the reductant system lamp bulb.

How to Fix

  • Replacement of reductant system malfunction bulb
  • Repair or replacement of open or shorted circuit between the PCM and instrument panel or other controllers
  • Replacement or reprogramming of PCM
  • Replacement of other controllers

If Error Code P065D is stored, and the reductant system malfunction lamp is operational, then you can suspect a defective or programming error in the PCM.