P24C9: particulate sensor temperature circuit reports an electrical fault

P24C9 is named temperature circuit high, but the cited electrical monitor includes more than a high signal. The sensor control unit checks the temperature-meander signal below 0.3 V or above 3.5 V, and also checks its reference voltage below 4.5 V. The strategy describes detection of a power short or open circuit.

Do not infer the fault direction from the title alone

Because the documented criteria include both low and high signal limits, the generic word “high” does not tell a technician which voltage was abnormal. The reference and measurement paths must also remain distinct; a low reference is different evidence from a high temperature signal.

ECM reporting requires the sensor bus relay on, no relay electrical fault, valid communication and no sensor-control-unit undervoltage fault. The counter is 24 consecutive failures or 24 out of 96 samples on a 100 ms task. The entry is Type B, two trips.

Verification

Use the applicable service data to identify the temperature-meander status and distinguish signal-range from reference failure. A plausible temperature display by itself does not establish that both electrical checks passed. Confirmation should include valid supply and communication plus a completed sensor-control-unit electrical test. The table does not supply external probe locations or establish which component requires repair.

Source and application limits

This explanation covers the cited 2025 GM monitor. Confirm the vehicle and calibration in its service information before applying these limits; inclusion in this file does not establish model compatibility. GM diagnostic parameters, PDF page 1499.