High emissions
Q: I am trying to reduce the high emissions produced by my nephew’s 2007 Vauxhall Astra 1.8 SRI Ecotec, which I think is engine code Z18XE. I’m getting fault code ‘P0105 – manifold absolute pressure/barometric pressure circuit’, but I don’t think this model has a MAP sensor as it is a Mafequipped engine. I have looked on the internet for a barometric sensor, to no avail.
The car shows –25% short term fuel trim at idle, which improves between –5 to –15% once the revs are raised upwards from 1500rpm; strangely though, the long term fuel trim remains at zero. I have tried cleaning the MAF, but it had no effect, then I tried running it unplugged, but that gave only slightly better figures. The 02 sensors do not get any switching while at idle – the readings displayed are fixed – but once the revs rise, the front one shows switching and voltage that appears normal. Unfortunately, the post-cat 02 sensor follows pretty much the same pattern as the front, so the cat is obviously contaminated. Dean Savage
A: According to Autodata, the full description of code ‘P0105’ is ‘Manifold absolute pressure (MAP) sensor/barometric pressure (BARO) sensor – circuit malfunction’. The code for the ‘barometric pressure (BARO) sensor – circuit malfunction’ may also be ‘P1105’.
As you have discovered, your Astra does not have a MAP sensor, but the code may have been raised by the information from the MAF sensor and TPS sensor being out of range. The air flow over the MAF sensor effectively gives the ECU the manifold pressure by combining the data with the information from the other sensors. Although you have cleaned the MAF sensor, this may still be the source of the problem code, which may not bring down the emission levels. As the second sensor is switching at the same rate as the first, this does indicate a faulty catalytic convertor, which I believe will need to be replaced.