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DTC codes / P24xx · Auxiliary emission controls / P242E

P242EExhaust Gas Temperature Sensor Circuit Intermittent or Erratic Bank 1 Sensor 3

P242E means the powertrain control module (PCM) has detected an intermittent or erratic signal from the exhaust gas temperature (EGT) sensor located after the diesel particulate filter (DPF) on bank 1, sensor 3. The PCM expects a smooth, predictable voltage change as exhaust temperature rises and falls, but the signal is jumping, dropping out, or behaving in a way that does not match engine operating conditions. This is a circuit or sensor fault, not a performance fault, so the vehicle may otherwise run normally.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • Illuminated check engine light, often with no other symptoms besides the warning light
  • Intermittent or fluctuating EGT readings on a scan tool live data stream
  • Reduced engine power or limp mode if the PCM cannot trust the EGT signal for DPF regeneration
  • Frequent or aborted DPF regeneration cycles, sometimes accompanied by increased exhaust smoke
  • Poor fuel economy or rough running if the faulty signal affects air-fuel and regeneration strategy
  • A stored P242E alone or alongside other EGT sensor or DPF-related codes

Common causes, most likely first

  1. Damaged, chafed, or corroded wiring between the EGT sensor and the PCM, especially near hot exhaust components
  2. Loose, contaminated, or corroded sensor connector pins causing an intermittent connection
  3. Failing EGT sensor element that goes open or shorted only when hot or during vibration
  4. Exhaust leaks upstream of the sensor allowing outside air to cool the tip erratically
  5. PCM connector or internal driver fault affecting the sensor signal circuit
  6. Aftermarket or incorrect sensor installed previously with a mismatched resistance curve
  7. Severe soot or carbon buildup on the sensor tip insulating it from exhaust gas temperature changes

How to diagnose and fix it

  1. Connect a scan tool and record live EGT sensor 3 data while wiggling the harness and connector to reproduce the erratic signal
  2. Visually inspect the sensor, connector, and wiring for chafing, heat damage, corrosion, or loose pins, and repair as needed
  3. Check for exhaust leaks at the DPF and sensor mounting boss, and reseal or repair any leaks found
  4. Measure the sensor resistance cold and compare it to the manufacturer's specification, then repeat after warming the engine
  5. Backprobe the signal circuit at the PCM and check for stable voltage or resistance while tapping the harness
  6. Replace the EGT sensor if wiring and connectors pass inspection but the signal remains erratic
  7. Clear the code and perform a road test with live data monitoring to confirm the signal is stable and the code does not return

What intermittent EGT codes really mean

  • An intermittent EGT code is more often a wiring or connector problem than a failed sensor, so replacing the sensor first frequently does not fix the fault.
  • The sensor can test perfectly on a cold engine and only fail when hot, so resistance checks must be repeated at operating temperature.
  • A small exhaust leak at the DPF or sensor boss can cool the sensor tip unevenly and set an erratic code without any electrical fault.
  • This code does not always mean the DPF is failing; a bad EGT signal can prevent regeneration and cause secondary DPF codes that disappear once the sensor circuit is repaired.
  • Heavy soot coating on the sensor tip can slow its response enough to trigger an erratic signal even though the sensor element itself is still good.

Can I keep driving with P242E?

The vehicle is usually safe to drive short distances because this is a signal fault rather than a mechanical failure, but avoid long trips and heavy loads until it is repaired. Continued driving with an erratic EGT signal can block DPF regeneration and lead to a much more expensive filter replacement.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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