P0646
A/C Clutch Relay Control Circuit Low
P0646 is an OBD-II diagnostic trouble code meaning: A/C Clutch Relay Control Circuit Low. Common causes: short circuit of the relay control wire to ground, clutch relay malfunction (internal short circuit). Estimated repair cost: $3–222.
Symptoms
- Check Engine light comes on
- Air conditioner won't turn on
- Air conditioner relay does not click when turned on
- Warm air comes from the air ducts
- Other air conditioning system codes are also possible
Causes
- Short circuit of the relay control wire to ground
- Clutch relay malfunction (internal short circuit)
- Poor ground connection of ECU or relay
- Malfunction of the ECU output stage (relay control)
- Damage to wiring insulation
How to Fix
- Check the voltage at the relay control contact with the air conditioner on
- Replace A/C Relay
- Check the control wire from the ECU to the relay for a short to ground
- Check the quality of the ECU mass connection
- If the code remains unchanged after replacing the relay and checking the wiring - ECU diagnostics
Related codes
Error P0646 by Vehicle Brand
FAQ
What does the P0646 code mean?
P0646 is an OBD-II diagnostic trouble code that indicates: A/C Clutch Relay Control Circuit Low
What causes a P0646 error code?
The most common causes of P0646 include: Short circuit of the relay control wire to ground; Clutch relay malfunction (internal short circuit); Poor ground connection of ECU or relay; Malfunction of the ECU output stage (relay control).
How do I fix a P0646 diagnostic trouble code?
To fix P0646: Check the voltage at the relay control contact with the air conditioner on. Replace A/C Relay. Check the control wire from the ECU to the relay for a short to ground. For a complete diagnosis, use an OBD-II scanner.
Is it safe to drive with P0646?
Yes, but get it checked soon
How much does it cost to fix P0646?
The estimated repair cost for P0646 is $3–222. Actual cost depends on your vehicle, location, and labor rates.
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