Fault codes
Code P0420: catalytic converter at fault, do you really need a new one?
Code P0420 does not always mean a dead catalytic converter. The real causes, the checks to do before you pay, typical costs and practical advice for drivers.
Fault codes
The most common fault codes explained in detail: what they mean, whether to worry, the causes to check in order and the indicative cost of repairs.
Fault codes
Code P0299, turbo underboost: the checks to make before accepting a turbo quote
Code P0299: the turbo pressure is too low, but the turbo itself is rarely the first culprit. The checks to make in order, before paying for a brand-new turbo.
Fault codes
Code P0171 / P0174: lean mixture, the 5 causes to check
P0171 and P0174 signal a lean mixture. Air leak, MAF sensor, injectors, fuel pump: here is the order to search in and how to use the fuel trims to find it.
Fault codes
Codes P0300 to P0306: misfires, finding the faulty cylinder
P0300 = random misfires, P0301 to P0306 = misfire on cylinder 1 to 6. Spark plugs, coils, injector or compression: the simple method to isolate the cause.
Fault codes
Code P0335 / P0340, crankshaft and camshaft position sensors: the car stalls or will not start
P0335 (crankshaft sensor) or P0340 (camshaft sensor): why the engine stalls or will not start, the rev counter test and the real causes to check, in order.
Fault codes
Code P0128 thermostat: confirm it with the coolant temperature in real time
Code P0128 often blames the thermostat, sometimes the sensor. A simple test: follow the coolant temperature during 10 minutes of driving, then compare it.
Fault codes
Code P0401: clogged EGR valve, clean it or replace it?
P0401 (insufficient EGR flow) mostly affects diesels and petrol cars used in town. Symptoms, causes, cleaning, and the cost of replacing the EGR valve.
Fault codes
Code P0380 / P0670 glow plugs: hard cold starts, what OBD2 tells you
Codes P0380, P0670 to P0678 on a diesel: glow plug, glow plug control unit or wiring? The tests to do before replacing all four glow plugs, and the costs.
Fault codes
Code P0101 / P0102: mass air flow sensor, clean it before replacing it
P0101 (MAF signal out of range) and P0102 (signal too low): air filter, intake leak, dirty sensor or dead MAF? How to check it, and what it costs.
Fault codes
Code P0455 / P0442: evaporative system leak, check the fuel cap first
P0455 (large leak) and P0442 (small leak) in the EVAP system: the fuel cap is the number one cause. What to check before you take the car to the garage.
Fault codes
O2 sensors P0130 / P0135 / P0141: sensor heater, one of the most common codes after the catalytic converter
Codes P0130, P0135, P0141: dead O2 sensor, failed heater or wiring? How to tell using the live sensor voltage, before you pay for a brand-new O2 sensor.
Fault codes
Code P2002 / P2463: diesel particulate filter, regeneration or replacement?
P2002 (DPF efficiency below threshold) and P2463 (soot build-up) on a diesel: short trips, pressure sensor, additive. How to avoid a €1,500 replacement.
Fault codes
Code P0087 / P0191: diesel fuel pressure, from the filter to the HP pump
P0087 (rail pressure too low) and P0191 (implausible rail pressure sensor) on common rail diesels: fuel filter, HP pump, regulator, injectors. Checks and costs.
Fault codes
Code U0100, lost communication: bad contact, weak battery or failed control unit?
Code U0100: a control unit can no longer hear the engine on the CAN network. Battery, earth, connector, added alarm or real failure: the order of the checks.