P0C18 code meaning
Drive Motor B Position Sensor Not Learned
Powertrain system Generic code P0Cxx codes Check engine light
What P0C18 means
P0C18 is the motor B version of P0C17: the resolver offset of the second motor has not been learned and no valid earlier value is stored. GM performs the learn at key-off; it fails if motor speed exceeds 50 rpm, DC voltage stays below 192 V, phase current stays below 15 A or the learn takes longer than 1.4 s. The Volt tables rate it Type A, one trip, the 2012 two-mode trucks Type B, two trips. GM bulletin 21-NA-218 notes that when P0C17 and P0C18 set together, a programming event is needed to allow a wide position sensor learn, and that missing high voltage at the drive motor control module can be the reason. P0C4F reports a learned value beyond its limit.
P0C18 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 8 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0C18
- Malfunction indicator lamp after a repair or module programming
- Reduced propulsion or vehicle will not enter ready mode
- Motor B unavailable for driving or charging
Common causes of P0C18
- Most likelyOffset learn not completed after replacing the inverter, motor B or its resolver
- PossibleNo high voltage at the drive motor control module, e.g. contactor fault or disconnected HV cable
- PossibleControl module needs reprogramming to enable a wide position sensor learn
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Drive motor b position sensorHybrid control module
What each part of P0C18 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| C | Area: hybrid propulsion. |
| 18 | The exact fault in that area. |
What to do next
- Note P0C18 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0C18
What does P0C18 mean?
P0C18 means "Drive Motor B Position Sensor Not Learned". P0C18 is the motor B version of P0C17: the resolver offset of the second motor has not been learned and no valid earlier value is stored. It is a generic code, so it means the same on every make.
Is it safe to drive with P0C18?
Drive gently and only to a workshop. With P0C18 the car can go into limp mode (reduced power) to protect itself.
Will P0C18 fail an emissions test?
Yes, it can. P0C18 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0C18 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 8 hours of work. This is a job for a workshop.
Will P0C18 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.