Diesel Trouble Codes

P2609 — Intake Air Heater 'A' Circuit High (6.7 Cummins (EGR + DPF, pre-SCR))

P2609 on 6.7 Cummins 2007.5–2012 means the PCM has detected voltage in the intake air heater 'A' circuit higher than expected. This platform uses a grid heater…

Updated September 2, 2026

What it means

The powertrain control module has detected voltage in the intake air heater ‘A’ circuit that is higher than the expected range. Typical on this platform: 6.7L Cummins 2007.5-2012 EGR+DPF pre-SCR, CP3, in-tank lift pump, HE351VE VGT electric actuator, grid heater cold start, no SCR/DEF, mechanical thermostat, gear timing, MAP primary.1

Most likely causes

  1. Grid heater relay contacts welded / stuck closed causing continuous high voltage to the heater element — The intake air heater ‘A’ circuit is commanded by a relay; welded contacts keep the grid heater energized and the PCM sees high circuit voltage. This is the most common electrical cause for P2609 on the 6.7 grid-heater system.1
  2. Short to voltage in the grid heater power feed or relay control wiring — Chafed harness or pinched wire feeding battery voltage to the heater circuit raises sensed voltage above expected range.1
  3. Faulty grid heater relay or driver circuit internal to the PCM — A failed relay coil or PCM driver can hold the circuit high; the PCM monitors the heater ‘A’ circuit for over-voltage conditions.1
  4. Failed / internally shorted grid heater element drawing abnormal current and raising circuit voltage feedback — A shorted element can pull the circuit voltage high on the sense side, triggering the high-circuit detection.1

How to diagnose

  1. Verify code P2609 is present and check freeze frame for ambient/engine temperature and run time.
  2. Inspect grid heater relay and fuse for signs of heat damage, corrosion, or welded contacts; test relay operation with a scan tool bi-directional command if available.
  3. Visually inspect grid heater power and control wiring from battery, relay, to intake manifold heater for chafing, melting, or shorts to power; pay attention to areas near the intake and valve cover.
  4. Measure grid heater resistance and isolation to ground; compare to service spec and look for a shorted element.
  5. Check PCM grid heater driver command and circuit voltage with a lab scope during key-on and cranking; confirm voltage stays within expected range and drops when commanded off.
  6. If wiring and relay test good, evaluate PCM control circuit for internal fault after confirming power/ground integrity to the PCM.
  7. Clear codes, perform a cold-start drive cycle and re-check for P2609 recurrence.

Parts and tools you may need

Rough cost and difficulty

Parts vary by condition; grid heater relay and wiring repairs are typically lower cost than replacing the intake grid heater assembly or PCM. Labor depends on access and diagnostic time.

When to see a pro

If the grid heater circuit shows signs of thermal damage, melted harness, or repeated relay failure, have a diesel technician inspect for underlying over-current conditions. Do not bypass or modify the grid heater circuit. If PCM driver fault is suspected, professional diagnosis is required before PCM replacement.

Sources

  1. Curated DTC seed — 6.7 Cummins (EGR + DPF, pre-SCR) (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎