BMW E46 mixture codes P0171 and P0174 (system too lean)
316i318i320i325i328i330i330xi
What causes E46 codes P0171 and P0174?
The codes mean the mixture is too lean. The most common cause is an intake leak, not the lambda sensor. Other causes include a faulty mass air flow sensor (MAF), too low fuel pressure and a leaking crankcase vent (breather).
How do you find the cause of an E46 lean mixture?
Start with a smoke test, which finds intake leaks fastest. Then check the fuel pressure at the rail (about 3.5 bar), the mass air flow sensor and the fuel trims with an OBD2 reader. The trims should be within about ±5 %.
Does the E46 lambda sensor need replacing when a mixture code appears?
Usually not. The lambda sensors of the M52TU and M54 rarely fail, so check for leaks and the breather parts first. If you suspect the front lambda, swap the sensors between the banks: if the fault moves, the sensor is faulty.
Related articles
BMW E46 engine oil choiceBMW E46 manual gearbox and rear axle oilBMW E46 oil light on: oil level sensorBMW E46 camshaft position sensor faultBMW E46 VANOS seal replacement and VANOS faultsBMW E46 ABS/ASC pump unit fault and fault code 113BMW E46 DSC and ASC light onBMW E46 ABS wheel speed sensor fault and code 49