What it means
The intake air heater B circuit voltage is above the expected level. This can result from a short to voltage or another circuit fault.
At a glance
- Usually lights the check-engine light
How it works
Heater B is the secondary intake air heater circuit on a diesel engine, used to support cold starts. The controller monitors its circuit voltage and sets P2608 when voltage is higher than expected, such as when the control wire contacts a battery supply or the relay coil is open. The heater may not operate correctly, so cold starts can take longer and produce rough running or smoke.
Common causes
Most likely first.
- Control wire shorted to a B+ supply
- Open 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 determine whether the high-voltage reading occurred when heater B was commanded on or off.
- Inspect the heater B harness and connectors for a wire touching a battery feed, damaged insulation, corrosion, or loose pins.
- Following the manufacturer's isolation procedure, check the control wire for a short to a B+ supply.
- Test the heater B relay coil for an open circuit and inspect the heater grid and relay connections.
- If the wiring and relay pass, measure circuit behavior during a heater command using the manufacturer's procedure to identify the source of the high reading.
Common fixes
- Repair wiring shorted to a battery supply.
- Clean and secure corroded or loose heater B connections.
- Replace the heater B relay if its coil is open.
- Replace the heater B grid if testing confirms it has failed.
Can I keep driving?
If the engine runs normally, short trips in mild weather may be possible, but cold starts can be difficult and smoky. Have the circuit repaired before depending on the vehicle in cold conditions.
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.