Steve Rothwell answering your ENGINE MANAGEMENT queries
Sensor data
Q Could you provide advice on sources of expected sensor performance data that could be used to compare against actual live sensor data? I wanted expected parameters for a 2007 Citroën C2 1.6, although even generic expected performance data for sensors is likely to be helpful given my limited knowledge for interpreting sensor data.
My Citroën’s in-car display is currently providing the message ‘Anti-Pollution system faulty’. However, no engine fault codes are logged when reading an OBDII scan tool.
I presume the dealer Lexia software would recognise and describe the fault; however I hoped that analysing the car’s sensor data – obtained using my current scan tool – against expected parameters would diagnose potential causes of the in-car display fault message.
A For the anti-pollution system message to be displayed, there should also be a code stored in the engine control module. This would normally be readable using an EOBD diagnostic scanner, although when gremlins are present I have seen vehicles not sticking to the rules and making any attempted diagnostics more difficult.
Because Citroën do expect their garages to have the full diagnostic equipment, the Citroën workshop manual does not give the individual reading expected from the sensors.
Likewise, Autodata do give the codes expected from a failing sensor, but do not give the readings that would be expected, and as the CO, HC and idle speeds are not adjustable, there is no data on these that would assist in the diagnosis.
Starting with the basics, if you do have live data on your scanner, then the first point to check is the air and coolant temperature sensor readings, these are easily checked and should be around the ambient air temperature and the correct running coolant temperature, with the engine up to running temperature this would be around 90°C. The air temperature reading will rise due to the heat of the engine.
If the O2 sensor data can be read on the scanner, then the upstream sensor should be seen to fluctuate between 0.2V to 0.8V as the ECU alters the mixture, whilst the downstream sensor should remain constant at around 0.45V.
But as noted earlier, if the ECU is correctly reading the sensors any incorrect data should flag up a fault code that can be read off.
FORD FOCUS
Q My trusty 20-year-old Citroën C15 van failed it’s last MOT due to terminal bulkhead corrosion around the master cylinder and, needing a quick replacement, I found a Ford C-MAX diesel, which was a lot cheaper than the equivalent Transit Connect. Not really what I wanted as not a van and a little too wide for one place I go to, but needs must, etc. The van use is private, not business.
Anyway, very nice vehicle to drive, it’s a 2010 vehicle (2003-10 model) with
