P24AF: Particulate Matter Sensor Circuit Range/Performance

P24AF tests whether the particulate matter sensor behaves plausibly while it burns itself clean. During that heated phase the electrodes must show a small but definite current, and the heater must change the signal in an expected way. Ford's 2023 diesel summary sets P24AF when the current during sensor regeneration at 770 to 800 °C stays below 0.094 µA, judged over 120 s. VW's 2014 Touareg list uses the code when the accumulated change in heater voltage is no more than 0.25 V. A sensor that no longer reacts cannot detect a cracked or removed filter, which is why CARB requires this check. GM handled P24AF together with P24AE on 2014 and 2015 Cruze diesels under special coverage 16018. P24AE is the electrode circuit fault, P24B3 the heater circuit.

Symptoms

• Malfunction indicator lamp on
• Often no change in driveability

Most likely causes

• Sensor element aged or glazed, no longer responding
• Sensor heater weak so the regeneration temperature is not reached
• Element cracked by condensate after cold start

What to check, in order

Start with the simplest. You can tick off each step.

1. Read the soot load and differential pressure with a scanner
2. Compare the reading with other engine data while varying the engine speed.
3. Check the differential pressure sensor's hoses
4. Check the temperatures before and after the filter
5. Fix any fuel injection or EGR codes before regenerating
6. Perform a regeneration while driving or at a repair shop when the diagnosis allows it

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P24AF means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 4: Emissions
• AF: Specific fault in that system

Frequently asked questions

Can I keep driving with code P24AF?

If the light is on steadily, take a highway drive or go to a repair shop soon. If the car is in limp mode or the light is flashing, do not push the engine.

What causes code P24AF?

The most common causes are: sensor element aged or glazed, no longer responding; sensor heater weak so the regeneration temperature is not reached; element cracked by condensate after cold start.

Related codes

• P24AEParticulate Matter Sensor Circuit
• P24B0Particulate Matter Sensor Circuit Low
• P24B1Particulate Matter Sensor Circuit High
• P24B3Particulate Matter Sensor Heater Control Circuit/Open
• P2002Diesel Particulate Filter Efficiency Below Threshold (Bank 1)

Sources

• fordservicecontent.com: obd summary diesel 2023
• static.nhtsa.gov: MC 10074008 2280
• static.nhtsa.gov: MC 10130682 9999
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.