Motor Relay Control Circuit Low
The motor relay control circuit is sending a low signal, indicating a malfunction.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
Inside the computer, when it wants to activate a motor, like for a brake booster or a pump, it sends out a signal. If the signal is too low (usually less than 5 volts) when it should be higher, it thinks there's a problem.
What the computer is actually seeing
The computer checks the voltage of the motor relay control circuit. It expects a voltage higher than 5 volts but sees a lower reading.
What a healthy reading looks like
The relay control circuit should have a voltage between 10-12 volts when powered and should switch on/off properly within a few milliseconds.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Inspect the wiring and connectors for the motor relay. Look for frays, breaks, or corrosion.
- 22. Use a multimeter to check the voltage at the relay when the system is activated. It should be above 10 volts.
- 33. If voltage is low, check for shorts to ground or battery in the wiring.
- 44. Test the relay itself by swapping it with a known good relay, then check for proper operation.
- 55. If the relay is good and wiring is intact, check the control module for faults.
Common causes
- Faulty motor relay
- Wiring issues (shorts or opens) in relay circuit
- Bad ground connection
- Faulty module or control unit
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It’s moderate severity. You might experience decreased performance. Fix it soon.
Will this code come back after clearing it?
It can return if the underlying issue isn't resolved.
Why does this code pair with C0856?
They often relate to the same circuit, indicating issues with the motor relay control system.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →