Owner experience. For the MAP sensor, vacuum leaks and the other sensor faults see MAP, boost and lambda sensor faults, and for reading codes see Reading fault codes.
A Turbo owner (2014, with a VXR turbo fitted) had hesitation on gentle acceleration. At low revs and light throttle the boost would build to a steady 15 psi, run rough for a few seconds, then drop to 0 psi. It was also very hesitant pulling away from a standstill. A new MAF made no difference, and a code reader then showed P0130 (O2 sensor circuit, bank 1, sensor 1, the front sensor).
- What the live data showed. After a minute or so the sensor reading and then the fuel trims flat-lined until the car was restarted. One owner says that is probably the ECU dropping into open loop and ignoring the sensor, which fits a P0130 and means replace the sensor. Another owner says a flat line would suggest a loom problem. The thread didn't settle which.
- The fix. A new Bosch pre-cat lambda sensor (about £50). It peaked at about 0.7 V instead of 1.1 V and updated more often, it kept working after five minutes, the hesitation and the partial-throttle judder went and power on higher loads improved. After he reset the fuel trims the ECU needed to relearn, and he noticed a slight pull-back on sharp high-load runs in second gear, which he hoped would settle. One owner got the same code and a new front sensor fixed it, with no symptoms other than the warning light.
- What is normal. The front sensor is a narrowband type that works in a narrow range, roughly 14.1 to 15.5 AFR, and is used mainly at idle and very low loads (one owner). It should swing between about 0.2 V and 0.8 V, from slightly rich to slightly lean about once a second, once the engine is fully warm (the sensor only works above about 350°C). One owner quoted the sensor maker as saying that at about 2,000 rpm it should switch in about 300 milliseconds. An OBD reader samples slowly so it can look slower. The bouncing is correct behaviour.
- How the ECU uses it. One owner explains that the fuel is made richer or leaner by steps depending on the lambda reading ("bang-bang" control), and the trims it learns are used in open loop under high load.
- P0130 has several variants. A freeze-frame read helps: high voltage (above 1.5 V), low voltage (below 60 mV), slow response, or the control limit reached lean or rich for 18 seconds (the list from one owner).
- Brand. One owner says prove it is the sensor first, and then buy a Bosch one rather than an unbranded part. Two later replies preferred genuine parts over a high-street parts chain's own range, though another thought a Bosch-branded part from the chain should be fine.
- On a supercharged car, an owner recommends fitting a new O2 sensor anyway when running an OBD tuner. His had no fault codes, but the car felt better and the fuel trims were lower afterwards (about £70).
- For the post-cat sensor, see Post-cat lambda sensor replacement.
Help wanted
We don't know the Bosch part number that matches each engine, or what separates a genuine sensor from the cheaper ones owners compared. If you have both, please tell us.