This week I'm taking a look at a couple of common OBD codes that can cause a check engine light to illuminate. A lit CEL usually leads to a state inspection or emissions fail but the good news is a lot of CEL problems are easy DIY fixes. The car in question here is a BMW X5 with the M54 engine. The same codes and parts apply to most other BMW models from this period, just the location changes. Remember if you don't have an OBD reader then many auto shops will read the codes for free for you.
Purge Valve
Codes P0443, P0444 and P0445 usually refer to the same piece - the evaporative purge valve. This is a piece that sits between the intake manifold and the charcoal canister connected to the fuel system. The valve opens electronically to allow fumes from the canister to burn off in the engine. The three codes refer to a general fault, the circuit stuck open or the circuit stuck closed respectively. In theory the wiring can cause these codes but unless there is obvious damage it is usually the valve itself that has failed and needs replaced.
Access is fairly easy on the M54 engine - a flat head screwdriver and 10mm socket are all that are needed. Remove the two airbox bolts (left side of engine bay), undo the air intake and just place to the side (wiring can remain connected). The valve should then be visible - it's held on with a simple bushing - just pull to remove. The hoses are also just push fit - so just swap out old for new.
Manifold Air Temp Sensor
Codes P0110 to P0114 refers to suspected failure of the air temperature sensor that sits inside the manifold. This is primarily used to fine tune fuel trim, but rough idle can also be felt in some cases if this fails. Access is good on the M54 engine - you just need a 10mm socket to remove the top plastic engine cover. The sensor is on top of the manifold with a 2 wire electrical connector. A simple plastic clip holds it in place, but as it's likely been there since the car was made you may have to put in some effort to remove it! The replacement can then slot straight in.
