Powertrain, generic (extended)

P24C9 Particulate Matter Sensor Temperature Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Broken temperature lead near the sensor body
Temperature line shorted to a voltage source
Reference voltage of the temperature circuit too low

Symptoms

  • Malfunction indicator lamp on
  • Particulate filter monitor does not complete

Repair estimate

DifficultyMediumDIY possible
Parts and labour€100–700
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

particulate matter sensor

Related codes

P24C6P24C7P24C8P24CA

References: gsi.ext.gm.com, law.cornell.edu.