Intake Air Heater "B" Circuit Low
The intake air heater B circuit is detecting a low voltage or open circuit condition, preventing the heater element from warming incoming air to the engine. This code typically sets in diesel engines or cold-weather gasoline engines equipped with intake air heating systems, affecting cold-start performance and engine reliability.
What You Might Notice
- Engine cranks longer than normal or won't start in cold weather
- Check Engine Light illuminated
- Rough idle at cold temperatures
- Engine stalling during cold starts
- Reduced engine performance in cold conditions
Most Common Causes
- 1
Faulty Heater Element Relay
The relay controlling the intake air heater circuit is stuck open or has failed, preventing voltage from reaching the heating element.
- 2
Defective Intake Air Heater Element
The heating element itself is burned out, broken, or has developed an internal open circuit, blocking current flow.
- 3
Corroded or Damaged Connector
Corrosion, loose pins, or physical damage to the heater circuit connector is creating poor electrical contact or an open circuit.
- 4
Damaged Wiring or Faulty Temperature Sensor
Broken wires, damaged insulation, or a faulty temperature sensor providing incorrect input can cause the PCM to detect a low-voltage condition.
How to Diagnose It
- 1
Check Faulty Heater Element Relay — The relay controlling the intake air heater circuit is stuck open or has failed, preventing voltage from reaching the heating element.
- 2
Check Defective Intake Air Heater Element — The heating element itself is burned out, broken, or has developed an internal open circuit, blocking current flow.
- 3
Check Corroded or Damaged Connector — Corrosion, loose pins, or physical damage to the heater circuit connector is creating poor electrical contact or an open circuit.
- 4
Check Damaged Wiring or Faulty Temperature Sensor — Broken wires, damaged insulation, or a faulty temperature sensor providing incorrect input can cause the PCM to detect a low-voltage condition.
How to Fix It
- 1
Inspect and Replace Heater Relay
Locate the intake air heater relay in the engine bay fuse/relay block, test it with a multimeter, and replace if faulty. Verify relay contacts are making proper connection.
- 2
Test and Replace Intake Air Heater Element
Remove the intake air heater element from the air intake manifold or ducting, test resistance across the heating element using a multimeter, and replace if open or resistance is infinite.
- 3
Repair Wiring and Connectors
Inspect the wiring harness between the relay and heater element for damage, corrosion, or loose connections. Clean connector terminals with contact cleaner, repair damaged insulation with electrical tape, or replace corroded connectors.
- 4
Test Temperature Sensor and PCM
Use a scan tool to verify the intake air temperature sensor is reading correctly; replace if faulty. If wiring and heater element test good, have the PCM tested or replaced by a qualified technician.
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