Faulty or worn main power relay (ECM/PCM relay) with poor contacts; Corroded, loose or burnt terminals in the relay socket or fuse box; Blown fuse or fuse with high resistance in the relay output or sense feed; Open circuit, high resistance or short to ground in the sense wiring between the relay and control module; Weak battery, poor battery terminals or charging system fault causing low supply voltage; Poor control module power or earth connections; Internal fault in the control module sense input.

P0689

ECM/PCM Power Relay Sense Circuit Low.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
89: FaultThe specific fault in that area

What it means

P0689 means the engine or powertrain control module has detected a low voltage on the sense circuit that monitors the main power relay's output. The control module expects to see battery voltage on this circuit shortly after the relay is commanded on, or while it is held on, and it saw a lower voltage than expected. The exact relay layout and circuit design vary by vehicle, so the wiring details depend on the model and engine.

Symptoms

Engine cranks but fails to start, or starts intermittently
Engine stalls or cuts out while running
Malfunction indicator lamp on
Other warning lights or multiple unrelated fault codes stored
Loss of communication with the control module at times
Control module powers down late or the car drains the battery

Possible causes

Faulty or worn main power relay (ECM/PCM relay) with poor contactslikely
Corroded, loose or burnt terminals in the relay socket or fuse boxlikely
Blown fuse or fuse with high resistance in the relay output or sense feedlikely
Open circuit, high resistance or short to ground in the sense wiring between the relay and control modulepossible
Weak battery, poor battery terminals or charging system fault causing low supply voltagepossible
Poor control module power or earth connectionspossible
Internal fault in the control module sense inputrare

How to diagnose

Read all stored codes and freeze frame data, noting battery voltage, engine speed and conditions when the code set, and check for other power supply or communication codes
Test battery condition and charging voltage, and inspect the battery terminals and main earth straps for tightness and corrosion
Check the relevant fuses visually and test them for voltage drop under load, using the vehicle wiring diagram to identify the right ones
Inspect the main relay, its socket and the fuse box for heat damage, corrosion, green deposits or water ingress
Swap-test or bench-test the relay using a known good one of the same specification, and check coil resistance and contact operation
With the ignition on, measure voltage at the relay output and at the control module sense pin, comparing the two to find any drop
Check the sense wire for continuity, resistance and short to ground with the module and relay disconnected, following the wiring diagram
Check the control module power and earth feeds under load, and only consider the module itself once all wiring and supply faults are ruled out

How to fix

Replace the faulty main power relay with one of the correct specification
Clean or repair corroded terminals and sockets, or replace the damaged socket or fuse box section
Replace blown or high-resistance fuses after finding out why they failed
Repair or replace damaged sense wiring, connectors or earth connections
Repair or replace the battery or charging system components if supply voltage is low
Replace or repair the control module only if testing confirms an internal fault, then have it programmed as the manufacturer requires

Can I keep driving?

High severity

Avoid driving until the fault is traced, as the engine may stall without warning or fail to restart, which is a safety risk in traffic. If it is intermittent and the car is running normally, drive only a short distance to a workshop.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.