Error Code P0689 is defined as ECM/PCM Power Relay Sense Circuit Low. This code is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. Some of the most common brands that come up with this code include Audi, Cadillac, Chevrolet, Dodge, Ford, Jeep, Volkswagen, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.
The PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) comes with a power relay that provides battery voltage safely to the right PCM circuits. It’s a contact type relay activated with a signal wire from the ignition switch. This type or relay usually uses five-wire design. Constant battery voltage is applied in one wire and ground to the other. A third circuit will carry the signal from the ignition switch, while the fourth will supply voltage to the PCM. The fifth wire, on the other hand, is the power relay sense circuit, and the PCM uses it to monitor the power relay voltage.
Error Code P0689 is stored when the PCM has detected an abnormal activity in the relay which supplies it with voltage. In this situation, the power relay sensor circuit lower than expected.
If the PCM determines an open power relay sense circuit, then this code will be stored and activate the Check Engine light.
The most common symptom of this code is the activation of the Check Engine light. However, in some cases, the Check Engine light may not come up, even when the code is stored. Other common symptoms include:
- Delayed or no start condition
- Some electrical accessories may be inoperative
There are several possible causes for this code, including:
- Damaged or defective PCM power relay
- Blown fuse or fusible link
- Open or shorted circuit between the PCM and power relay
How to Check
Like many codes, a good starting point for diagnosis for this code is to check with the TSB (technical service bulletins) for the specific vehicle. The problem could be a known issue, with a known fix provided by the manufacturer.
Get all stored codes and freeze frame data by connecting the scanner to the vehicle’s diagnostic port. Take note of this information in case the problem proved to be intermittent.
Then clear the codes and then take the vehicle for a test drive (if possible) until the code resets, or the PCM enters readiness mode. If the PCM does the latter, then the problem is intermittent, which means you have to wait for it to get worse before you can make a full diagnosis. If the code is UNABLE to reset on the other hand, and there are no driveability symptoms, then continue operating the vehicle normally.
Check with your TSB for the code stored, vehicle (make, year, model, and engine), and symptoms. This can help you in your diagnosis.
If the code RESETS immediately, then proceed on a thorough inspection of the wiring and connector system. Broken harnesses must be repaired, if not replaced.
If wiring and connectors look good and functional, then use the vehicle information to get the wiring diagram, connector pin-out charts, connector face views, and diagnostic flow charts. Once you have this information, make sure the PCM power supply relay get battery voltage by testing all fuses and relays.
If constant (or switched) voltage is nowhere to be found at the power relay connector, then trace the right circuit back to the fuse or relay from which it originates. Repair or replace defective fuses or fusible links as necessary.
If the power relay supply input voltage and ground are both present (on all right terminals), use the DVOM (digital volt/ohm meter) to test the relay output performance at the right connector pins. If the power supply relay output circuit voltage is not enough, then you can suspect a defective relay.
If the PCM power supply relay output voltage is right within the specifications (on all terminals), then test the corresponding relay output circuits at the PCM.
If a relay output voltage signal is discovered at the PCM connector, then you can suspect a defective or programming error in the PCM.
If there’s no relay output voltage signal at the PCM connector, then the problem is most probably caused by an open circuit.
To avoid misdiagnosis, fuses and fusible links must be tested with the circuit loaded.
Fuses and fusible links should be tested with the circuit loaded to avoid a misdiagnosis.
How to Fix
Depending on the diagnosis, common repairs for this code include:
- Charging the battery fully
- Repair of loose or damaged battery cables
- Replacement of the battery (if necessary)
- Replacement of damaged or blown fuses
- Repair of loose or shorted connections
- Repair or replacement of corroded or damaged electrical wires and related connectors
- Replacement of defective ECM/PCM relay
- Replacement of ECM
As with other codes, it’s important to clear all codes, test-drive the vehicle, and rescan to see if any codes reappear.
Since this code affects the driving operation of the vehicle, it’s considered serious. Thus, it’s recommended that this code must be addressed as soon as it appears.
The most common misdiagnosis of this code is replacing the ECM/PCM. It’s important to test and repair all possible symptoms first.