Intake Air Heater "B" Circuit High
P2608 indicates the intake air heater B circuit is reading higher than expected voltage or resistance. This system preheats incoming air on cold starts to improve combustion and engine startability, typically found on diesel and some gasoline engines. A high circuit reading suggests a faulty heater element, relay, or wiring issue.
What You Might Notice
- Engine difficult to start in cold weather
- Longer than normal cranking time
- Rough idle at cold temperatures
- Check Engine Light illuminated
- Engine stalling after cold start
Most Common Causes
- 1
Faulty heater element relay
The relay controlling the intake air heater may be stuck, burned out, or unable to properly switch the heater circuit. This prevents normal current flow or causes excessive voltage.
- 2
Defective intake air heater element
The heating element itself may be damaged, have increased resistance, or be failing. This causes abnormal voltage readings in the circuit.
- 3
Faulty temperature or circuit sensor
A malfunctioning temperature sensor or dedicated heater circuit sensor sends incorrect voltage signals to the PCM, triggering the code even if the heater is functioning properly.
- 4
Corroded or damaged wiring and connectors
Corrosion, breaks, or loose connections in the heater circuit wiring harness cause high resistance and abnormal voltage readings that the PCM interprets as a circuit high condition.
How to Diagnose It
- 1
Check Faulty heater element relay — The relay controlling the intake air heater may be stuck, burned out, or unable to properly switch the heater circuit. This prevents normal current flow or causes excessive voltage.
- 2
Check Defective intake air heater element — The heating element itself may be damaged, have increased resistance, or be failing. This causes abnormal voltage readings in the circuit.
- 3
Check Faulty temperature or circuit sensor — A malfunctioning temperature sensor or dedicated heater circuit sensor sends incorrect voltage signals to the PCM, triggering the code even if the heater is functioning properly.
- 4
Check Corroded or damaged wiring and connectors — Corrosion, breaks, or loose connections in the heater circuit wiring harness cause high resistance and abnormal voltage readings that the PCM interprets as a circuit high condition.
How to Fix It
- 1
Test and replace heater relay
Use a multimeter to test the intake air heater relay for proper resistance and switching operation. Replace the relay if it fails testing or shows signs of burning or corrosion.
- 2
Inspect and repair wiring harness
Visually inspect the intake air heater circuit wiring for cuts, abrasions, corrosion, and loose connectors. Repair any damaged sections and clean corroded connector terminals with electrical contact cleaner.
- 3
Test and replace heater element
Disconnect the heater element and measure resistance with a multimeter against manufacturer specs. If out of range or open circuit, replace the intake air heater element.
- 4
Replace temperature sensor if faulty
Test the intake air temperature sensor output voltage with a scan tool while the heater operates. If readings are incorrect or out of range, replace the sensor.
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