P0687

ECM/PCM Power Relay Control Circuit High

Car Fault Codes Engine computer & electrical

Can you still drive? With care, short trips only

Who can fix it? Needs a workshop

Typical repair time 15 minutes – 4 hours

Typical cost SAR 50 to 5,000

What it means

The engine computer (ECU) detected higher than expected voltage on the main relay control circuit, such as voltage present when the relay should be off. This can mean the relay is stuck or the wire is shorted to a voltage source, keeping power connected after the vehicle is switched off and draining the battery.

Symptoms4

Check engine light on.
Dead battery after the vehicle sits.
Some parts such as the fan or pump still running after the engine is off on some vehicles.
Occasional hard starting.

Possible causes5

Welded contacts inside the main relay.
Control circuit wire shorted to a voltage source.
Moisture or corrosion in the relay box bridging terminals.
Faulty ignition switch sending a constant signal on some vehicles.
Faulty control circuit inside the engine computer.

How to diagnose5

Switch the vehicle off and check after a few minutes whether the main relay is still energized.
Swap in an identical known-good relay and see if the code clears.
Measure voltage on the control circuit with the key off; voltage remaining after the shutdown delay points to a short or stuck relay.
Inspect the relay box and connectors for moisture.
Measure battery drain with the vehicle off.

How to fix5

Replace the main relay if its contacts are welded.
Repair the wire shorted to voltage and re-insulate it.
Dry out the relay box and clean corroded terminals.
Repair the ignition switch or engine computer if proven faulty.
Clear the codes and confirm the relay switches off after shutdown and the code does not return.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low for a relay or wire repair, and reaches the upper end only if the engine computer must be replaced and programmed.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

Why does my battery go flat with this code?

The main relay may stay on after the vehicle is switched off, keeping the computer and some parts powered and draining the battery.

Is it normal for the relay to stay on briefly after shutdown?

Yes. On many vehicles the computer holds the relay on for a short time to save its data, but staying on for a long time is not normal.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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