P0689: ECM/PCM Power Relay Sense Circuit Low

The engine module switches its main relay coil to ground (control circuit), reads the switched voltage back on a sense line and keeps the relay on briefly after ignition off to save learned values. P0689 means the sense voltage is too low although the relay is commanded on – the contact does not close or has high resistance, the sense line is open or grounded, or a fuse in the load circuit has blown. GM sets it at 5 V or less with more than 9 V supply in 5 of 6 samples at 1 s, lamp after two trips; GM Europe's V6 below 6 V for 1 s and the 2.0 L turbo below 5 V, both without the lamp. GM includes an open sense line here. Starting problems or stalling follow, and on Saab the throttle control, which uses this voltage, may go into limp mode.

Medium severity. Can I keep driving?It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

Symptoms

Check engine light (depending on the maker)
Starting problems or no start
Engine stalls or stumbles
Possibly electronic throttle limp mode

Most likely causes

Relay contact burnt or not closing, relay faulty
Fuse in the relay load or sense path blown
High resistance or corrosion in relay carrier, connector or wire
Weak battery

What to check, in order

Start with the simplest. You can tick off each step.

Check the battery and grounds
With the connector unplugged, check whether the signal wire is making contact with ground.
Clear the code and see if it returns
If it is a reference voltage code, disconnect sensors one at a time and see if the voltage recovers
Check whether a software update is available
Do not replace the control module without a full diagnosis

Good to know

Repair difficulty: easy
It can trigger limp mode.
It affects emissions.

What each character of P0689 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
6: Control modules and outputs
89: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0689?

It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

What causes code P0689?

The most common causes are: relay contact burnt or not closing, relay faulty; fuse in the relay load or sense path blown; high resistance or corrosion in relay carrier, connector or wire.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.