P24C9 code meaning
Particulate Matter Sensor Temperature Circuit High
Powertrain system Generic code P24xx codes Check engine light
What P24C9 means
P24C9 reports the PM sensor temperature reading stuck at the high end, which GM explains as a short toward supply voltage or a broken meander line. In GM's 25OBDG04A diesel table the sensor control unit checks the meander signal and its reference: a signal under 0.3 V or over 3.5 V, or a reference under 4.5 V, counts as a failure, and 24 failures in a row or 24 of 96 samples set a Type B code with two trips. Other makers reviewed here, such as Ford in its 2023 diesel summary, report out-of-range temperature signals under P24C6 instead. A broken pigtail lead near the hot sensor body is a common cause. While the temperature is invalid the heater control and the filter monitor are suspended. P24C8 is the low side, P24C7 the plausibility test.
P24C9 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of P24C9
- Malfunction indicator lamp on
- Particulate filter monitor does not complete
Common causes of P24C9
- Most likelyBroken temperature lead near the sensor body
- PossibleTemperature line shorted to a voltage source
- Less likelyReference voltage of the temperature circuit too low
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Particulate matter sensor
What each part of P24C9 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| C9 | The exact fault in that area. |
What to do next
- Note P24C9 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 P24C9
What does P24C9 mean?
P24C9 means "Particulate Matter Sensor Temperature Circuit High". P24C9 reports the PM sensor temperature reading stuck at the high end, which GM explains as a short toward supply voltage or a broken meander line. It is a generic code, so it means the same on every make.
Is it safe to drive with P24C9?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P24C9 fail an emissions test?
Yes, it can. P24C9 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 P24C9 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P24C9 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.