P23C4 code meaning
Engine Coolant Bypass Valve C Position Sensor Circuit Low
Powertrain system Generic code P23xx codes Check engine light
What P23C4 means
P23C4 says the angle reported by the bypass valve C position sensor has dropped below anything the sensor can produce in normal use, which GM traces to the signal line touching ground. GM's 2025 tables use the code on both its 3.0L Duramax diesel (25OBDG04B) and a gasoline family (25OBDG03B): the SENT sensor value must fall under 27 or under 50 counts respectively, for 4 seconds within a 5-second window, while SENT communication itself is healthy and the engine is not cranking. It is a Type B fault, so the lamp comes on after the second failing trip. With the feedback gone, the valve can no longer be positioned reliably and warm-up or cooling may suffer. The opposite case is P23C5; a wider position error is P26BB.
P23C4 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P23C4
- Engine warning lamp after two drives
- Bypass valve C position shown as implausibly low in live data
- Slow warm-up or unusual engine temperature
Common causes of P23C4
- Most likelyPosition sensor signal wire chafed against ground
- PossibleCoolant or water in the valve connector bridging the signal to ground
- PossibleDefective position sensor inside the valve actuator
- Less likelyMissing sensor supply so the output stays at its lowest value
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Coolant bypass valve c position sensor
What each part of P23C4 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 3 | Area: ignition system or misfire. |
| C4 | The exact fault in that area. |
What to do next
- Note P23C4 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 P23C4
What does P23C4 mean?
P23C4 means "Engine Coolant Bypass Valve C Position Sensor Circuit Low". P23C4 says the angle reported by the bypass valve C position sensor has dropped below anything the sensor can produce in normal use, which GM traces to the signal line touching ground. It is a generic code, so it means the same on every make.
Is it safe to drive with P23C4?
Drive gently and only to a workshop. With P23C4 the car can go into limp mode (reduced power) to protect itself.
Will P23C4 fail an emissions test?
Yes, it can. P23C4 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 P23C4 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P23C4 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.