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Demystifying Exhaust Error Codes

Diagnostic Trouble Codes can seem cryptic. Here are a few codes for exhaust issues we've seen at the garage lately, with a brief explanation of each.


One of our technicians at Portway MOT Centre, performing some diagnostic checks for a customer.
One of our technicians at Portway MOT Centre, performing some diagnostic checks for a customer.

P24C6 – Particulate Matter Sensor Heater A Control Circuit/Open


This code indicates an issue with the particulate matter (PM) sensor heater circuit. It may be open, shorted, or not functioning properly.


The heater is used to ensure the PM sensor operates accurately by maintaining it at the right temperature.


Common causes:

  • Faulty PM sensor

  • Damaged or corroded wiring/connectors in the PM sensor circuit

  • Blown fuse related to emissions system

  • Faulty Engine Control Module (rare)



P24AF – Particulate Matter Sensor Heater Performance


This code suggests that the heater on the PM sensor isn’t performing as expected; possibly not reaching the required temperature.


Common causes:

  • A failing or degraded PM sensor

  • Poor electrical connection or high resistance in the heater circuit

  • Software/firmware issue in the ECU (less common)



P046C – Exhaust Gas Recirculation (EGR) Sensor "B" Circuit Range/Performance


This code points to an issue with the EGR Sensor B, specifically, the sensor is sending a signal that is out of expected range or performing erratically. The EGR system is responsible for recirculating a portion of exhaust gases back into the intake to reduce NOx emissions.


Common causes:

  • Faulty EGR pressure/position sensor

  • Carbon buildup in the EGR valve or passages

  • Wiring issues (corroded, damaged, or shorted wires to the sensor)

  • Bad EGR valve (sticking or not moving properly)

  • Vacuum issues (on vacuum-controlled EGR systems)

  • ECU/software issue (less common)



Get Your Vehicle Issues Resolved


If you are having trouble with your exhaust or any other problem with your vehicle, contact one of our garages to arrange a booking. Once your car is on the ramp, our technicians will perform a free visual inspection and recommend any work required without charging you a penny. We can also run a full diagnostic test on your vehicle starting from as little as £51.


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