What it means
The intake air heater B circuit voltage is below the expected level. This can result from a short to ground or another circuit fault.
At a glance
- Usually lights the check-engine light
How it works
The intake air heater B circuit supplies the secondary diesel intake heater used to aid cold starting. The controller monitors circuit voltage and sets P2607 when it is lower than expected, which can happen with a control wire shorted to ground or a faulty relay coil. Heater B may then fail to warm the intake air, leading to hard cold starts, rough running, or smoke.
Common causes
Most likely first.
- Control wire shorted to ground
- Internal short in relay coil
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light
- Longer cranking or hard starting in cold weather
- Rough running or increased exhaust smoke after a cold start
How to diagnose it
- Record freeze-frame data and check whether the low-voltage fault appeared while heater B was commanded on.
- Inspect heater B wiring and connectors for chafing against ground, corrosion, moisture, or loose pins.
- With the circuit safely isolated as directed by the manufacturer, check the control wire for a short to ground.
- Test the heater B relay coil and grid for shorts or other faults using the manufacturer's procedure.
- If no short is found, check connector contact condition and circuit voltage under command to locate excessive resistance or a wiring fault.
Common fixes
- Clean and secure corroded heater B connector pins.
- Repair the control wire where its insulation is damaged or it is shorted to ground.
- Replace the heater B relay if its coil is internally shorted.
- Replace a faulty heater B grid if testing identifies it as the cause.
Can I keep driving?
Driving may be possible if the engine runs normally, but cold starts can be unreliable and produce more smoke. Avoid cold-weather trips until the low-voltage fault is repaired.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.