What does it mean?
The module has calculated that the charge air cooler is not removing as much heat from the compressed intake air as it should. It compares the temperature of the air entering the cooler with the temperature leaving it, taking ambient temperature, vehicle speed and engine load into account, and expects a certain drop across the cooler under load. When the measured drop stays below the modelled value for long enough, this efficiency code is stored.
Hot intake air reduces power, raises the risk of knock on petrol engines and increases emissions on diesels, so the module often limits boost or retards timing to protect the engine. The cause can be airflow, coolant flow on water-cooled systems, internal fouling of the cooler, or simply an intake air temperature sensor that no longer reads correctly.
Symptoms
- Reduced power and flat acceleration, especially on long climbs, when towing or in hot weather
- Intake air temperatures in live data that stay far above ambient under load
- Knock retard or reduced boost on petrol engines, black smoke on diesels
- Higher fuel consumption
- MIL on, sometimes together with boost or intake temperature codes
Likely causes
- Airflow to the cooler blocked by leaves, mud, insects, plastic bags or bent cooling fins
- Oil fouling inside the cooler core from a leaking turbocharger seal or heavy crankcase ventilation carry-over
- On water-to-air systems, low coolant level, air in the low temperature circuit or a weak auxiliary coolant pump
- Charge air cooler cooling fan not running where one is fitted
- Intake air temperature sensor drifted, contaminated with oil or reading slowly
- Leaking cooler core or a loose hose clamp that lets charge air escape
- Additional bodywork, badges or accessories fitted in front of the cooler restricting airflow
- Blocked condenser or radiator ahead of the cooler raising the air temperature that reaches it
How to fix it
- Log the intake air temperature before and after the cooler together with ambient temperature during a sustained load drive, and compare the actual drop with what is expected
- Verify the sensors first: after a long soak all intake and ambient temperatures should read within a couple of degrees of each other
- Inspect the front of the vehicle for debris, bent fins and anything fitted in front of the cooler
- Remove a hose and check the inside of the cooler for oil; a coated core cannot transfer heat
- On water-cooled systems check the low temperature circuit level, bleed it and confirm the auxiliary pump and fan operate when commanded
- Pressure-test the charge air system to find leaks that reduce both boost and cooling
- Clean or replace the cooler once it is proven fouled, then repeat the load test and confirm the temperature drop is restored