Faulty or sticking ECM/PCM power relay; Damaged wiring, short to voltage or chafed loom on the relay control circuit; Corroded, loose or water-damaged connectors or relay base terminals; Low battery voltage, poor earth or charging system fault upsetting the circuit readings; Blown or wrong-rated fuse, or a fault in the fuse and relay box; Internal fault in the ECM/PCM driver circuit.

P0687

ECM/PCM Power Relay Control Circuit High.

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
87: FaultThe specific fault in that area

What it means

P0687 means the engine or powertrain control module has detected a high voltage state on the control circuit for its main power relay. The module commands the relay on and off and monitors the circuit, and what it saw did not match the command, for example voltage present when it should have been low. The exact relay layout and the conditions for setting the code vary by model and engine.

Symptoms

Engine cranks but will not start, or starts and then stalls
Malfunction indicator lamp on
Intermittent loss of power or cutting out while driving
Engine control unit powering down late or not at all after switching off
Other warning lamps or stored codes appearing at the same time

Possible causes

Faulty or sticking ECM/PCM power relaylikely
Damaged wiring, short to voltage or chafed loom on the relay control circuitlikely
Corroded, loose or water-damaged connectors or relay base terminalslikely
Low battery voltage, poor earth or charging system fault upsetting the circuit readingspossible
Blown or wrong-rated fuse, or a fault in the fuse and relay boxpossible
Internal fault in the ECM/PCM driver circuitrare

How to diagnose

Read all stored codes and freeze frame data, noting any other power supply or communication codes, then record and clear only to see whether P0687 returns
Check battery condition and charging voltage, and inspect the battery terminals and main earths for tightness and corrosion
Visually inspect the relay, fuse box, and wiring to the ECM/PCM for water ingress, heat damage, chafing or previous repairs
Check the relevant fuses for condition and correct rating using the model's wiring diagram
Swap the relay with a known good identical one if the layout allows, or test the relay coil and contacts against the manufacturer's specification
Check the relay control circuit for short to voltage, open circuit and high resistance with the relay removed, following the wiring diagram
Check supply and earth feeds at the ECM/PCM connector, wiggling the loom while monitoring for intermittent faults
Only after all of the above, consider testing or replacing the control module, following the manufacturer's procedure

How to fix

Replace the faulty ECM/PCM power relay with the correct specification part
Repair or replace damaged wiring and fix any short to voltage on the control circuit
Clean or replace corroded connectors and relay base terminals, and cure any water ingress
Restore battery, charging and earth connections to good condition
Replace blown fuses only after finding and fixing the cause of the failure
Repair or replace the ECM/PCM if testing proves an internal driver fault, and have it programmed as required

Can I keep driving?

High severity

Avoid driving until it is diagnosed, as the engine may stall or cut out without warning, which is unsafe. If the car is running normally and the fault is intermittent, limit use to getting it to a workshop.

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