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Modern vehicles are equipped with multiple systems that work together to ensure your vehicle runs smoothly. These systems rely on computers like the powertrain control module (PCM) or electronic control module (ECM) to direct them and keep track of their functions.

Like any other computer system, a vehicle’s ECM and PCM can malfunction due to many reasons. P0689 is an error code related to a fault in the ECM or PCM’s power relay sensor circuit.

What Does the P0689 Code Mean?

Diagnostic trouble code (DTC) P0689 stands for “ECM/PCM Power Relay Sensor Circuit Low.” The code is set once your vehicle’s computer detects a possible problem with the relay that supplies it with voltage.

The PCM is in charge of controlling the powertrain, which includes the engine and transmission. It keeps track of parameters like engine speed, coolant temperature, and throttle position. The device also regulates outputs for the fuel injectors and ignition coils.  It receives data from all these components in the form of voltage signals.

If the PCM detects a low voltage condition on the power relay sense circuit, it will store the code P0689 code.

P0689 on a 2017 Chevrolet Camaro:

This is the description of the P0689 code from a 2017 Camaro:

There are 2 ignition voltage circuits supplied to the ECM.

One is supplied by the engine controls ignition relay, and the other is supplied by the ignition main relay.

The ECM monitors and compares the ignition voltage supplied by the two relays. Conditions for setting the code are as follows:

  • The engine controls ignition relay is commanded ON.
  • Ignition 1 signal voltage is greater than 11 Volts.
  • The engine controls ignition relay voltage at the ECM is not present or is very low.

Ignition Main Relay Diagram

illustration of ignition main relay waking up pcm
In the circuit shown in this diagram, the ignition main relay “wakes up” the ECM, which then grounds the ignition controls relay coil, sending power to the ignition coils and to a separate circuit in the ECM. These two feeds are compared, and should match. If the Controls Relay isn’t delivering voltage to the ECM, code P0689 is set. Note that there are a few different ways these systems are wired, and the example shown here is only one of the possible configurations. | Image Source: Richard McCuistian

Note: The definition of code P0689 might be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What Are the Common Causes of the P0689 Code?

  • Malfunctioning PCM relay
  • Circuit issues between the relay and PCM
  • Blown fuse or fusible link

What Are the Common Symptoms of the P0689 Code?

  • Possible “no start” condition/delayed start
  • Malfunctioning electric accessories
  • Driveability issues

How to Diagnose a P0689 Code

mechanic encounters p0689 code
P0689 is a generic code, but that doesn’t mean that there’s a universal solution for all affected vehicles.

P0689 is a generic code, but that doesn’t mean that there’s a universal solution for all affected vehicles. Remember that vehicles can be structured differently depending on their manufacturer. If you’re not familiar with the PCM and vehicle repair in general, we recommend taking your vehicle to a trusted mechanic for proper diagnosis.

How to Fix the P0689 Code

Repairing a P0689 trouble code can be difficult, especially if you lack the necessary skills and tools. If you are not an experienced auto DIYer, it may be best to take a trip to a reputable repair shop near you.

If you really want to fix the code yourself, we recommend consulting a repair manual or subscribing to an online repair database. These manuals contain information specific to your vehicle.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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