P0689Generic code

P0689 Code: ECM/PCM Power Relay Sense Circuit Low

The P0689 code means the control circuit of the engine computer power relay shows low voltage, which points to a short to ground or a loss of supply. It can cause a no start or an engine that shuts off while driving. Check the fuse, relay, connector and wiring before replacing any part.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$15 to $300
Difficulty
Medium
System
Computer and Outputs
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0689 code means

On many vehicles the engine computer gets its power through a main relay that the computer itself controls. It switches the relay on when you turn the key to run and keeps it on for a few seconds after you shut the engine off so the computer can save its data.

The computer watches the control circuit from its own driver transistor. The P0689 code tells you the voltage in that control circuit is low, which means a short to ground or a missing supply. Before you replace any part, check the fuse, the relay, the connector and the wiring, because those are the most common causes.

If the relay fails, the computer can lose power while you are driving (the engine shuts off) or it may not be able to save its data when you switch the car off. A relay that sticks closed keeps the computer powered up and drains the battery.

To confirm the fault, unplug the relay with the key on and watch what happens to the reading or the code. If the value jumps to the opposite extreme, the wiring is fine and the relay is the part pulling the signal to ground. If nothing changes, look for the short in the wire itself, starting where the harness rubs against the engine, the chassis or the exhaust.

P0689 code symptoms

  • Check engine light or another warning light on.
  • Engine will not start or shuts off.
  • Engine suddenly dies or will not crank at all.
  • Dead battery after the car sits for several days.

Likely causes of the P0689 code

  1. Control wire shorted to ground. The relay may stay on all the time, or the computer cuts the command to protect itself.
  2. Interrupted supply: a blown fuse, a faulty relay or a cut wire.
  3. Shorted relay coil. The resistance is far lower than specified.
  4. Connector with moisture, which creates a path to ground.

How to diagnose the P0689 code step by step

  1. Command the relay with the scan tool and check whether it responds.
  2. Check the fuse and the relay. Measure voltage on both sides of the fuse, and swap the relay with an identical one.
  3. Measure the supply at the connector. You should see battery voltage with the key on or when the relay is commanded.
  4. Measure the relay resistance and compare it with the manual. Also check the insulation to ground.
  5. Check the control wire for continuity all the way to the computer and for any short circuits.
  6. Swap in an identical relay to rule out the original one.
  7. Check that the relay turns off after shutdown, which should happen within a few seconds or minutes.

How to fix the P0689 code

  • Repair the connector, the wiring or the power supply.
  • Replace the PCM power relay if it does not respond when it has correct power and a correct control signal.
  • Clear the P0689 code and verify the repair with a test drive.

Technical reference data

  • 12 volt relay in the engine compartment fuse box.
  • Reference values only: check the manufacturer data for your vehicle.

Brand-specific notes

The source reports this code as frequent on Mazda, Ford and Volkswagen vehicles. The same fuse, relay, connector and wiring checks apply on all of them.

P0689 on Mazda

Frequent on Mazda. Start with the fuse and relay before replacing anything else.

P0689 on Ford

Frequent on Ford. Check the connector and the control wiring before you buy a part.

P0689 on Volkswagen

Frequent on Volkswagen. Test the relay and its supply first, since they are the most common causes.

Frequently asked questions about P0689

What does the P0689 code mean?
It means the control circuit of the engine computer power relay has low voltage. The cause is a short to ground or a loss of supply.
Can I drive with a P0689 code?
Only with caution. The engine can shut off without warning or fail to start, which is a safety risk in traffic, so get it checked soon.
What does the PCM power relay do?
On many vehicles the computer is powered through a main relay that it controls itself. It switches the relay on with the key and keeps it on for a few seconds after shutdown so it can save its data.
Do I always have to replace the part?
No. Check the fuses, relays, connectors and wiring first, because they cause most of these codes and cost very little to fix.
How much does it cost to fix P0689?
As a rough guide, between $15 and $300, depending on whether it is a fuse, a relay or a wiring repair.

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