P24C9: Particulate Matter Sensor Temperature Circuit High

What it means

Same as P24C6 with the signal voltage above the plausible range. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The PM sensor’s temperature element tells the control module whether the sensor is hot enough to measure soot after regeneration. This code sets when the temperature-circuit signal rises above the plausible range, often because the signal wire is shorted to a supply or has contacted a battery-positive source.

Common causes

Most likely first.

1. Signal shorted to supply
2. Connector pins corroded - high contact resistance
3. Supply wire pinched against B+ source

Symptoms

• Check-engine light on
• Particulate matter sensor or aftertreatment warning
• Emissions inspection failure

How to diagnose it

1. Check freeze-frame and live data to confirm the PM-sensor temperature signal is high while the code is active.
2. Inspect the sensor connector and exhaust-area harness for pinched insulation, chafing, corrosion, or a wire touching a power source.
3. Move the harness gently while monitoring live data to see whether the high signal changes with harness position.
4. Using the wiring diagram, test the signal circuit for a short to supply and inspect terminals for damage or poor contact.
5. If the circuit has no short to supply, test the PM sensor’s temperature circuit against the manufacturer’s specification.

Common fixes

• Repair a signal wire shorted to a supply or battery-positive source.
• Replace heat-damaged or pinched wiring and secure it away from power sources.
• Repair corroded or damaged connector terminals.
• Replace the PM sensor if its temperature circuit remains above range with sound wiring.

Can I keep driving?

The vehicle may be driveable if it runs normally, but the PM-sensor warning can remain and emissions monitoring may not work correctly. Avoid delaying repair, especially if other aftertreatment warnings appear.