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        General >> OBD Advice >> O2 error help
        
(Message started by: - Mike - on Nov 8^th, 2005, 8:11pm)

Title: O2 error help
Post by - Mike - on Nov 8^th, 2005, 8:11pm

Hi Chaps

Please can anybody shed some light on a small problem that arisen recently concerning two of the lambda sensors :-

P0138 & P0158

I've seen the error code list but this doesn't explain the possible reasons for the fault and I'm running out of ideas beyond simply replacing them.

Thanks

Mike

Title: Re: O2 error help
Post by Simmo on Nov 8^th, 2005, 10:45pm

Does this help?.http://www.fordscorpio.co.uk/codes.htm.

Title: Re: O2 error help
Post by scorpio_man on Nov 9^th, 2005, 6:59am

hi mike

i'd check the wiring first, as both codes are same, just on different banks.

Title: Re: O2 error help
Post by Eric_R on Nov 13^th, 2005, 2:27pm

Mike,
The page you need is http://www.fordscorpio.co.uk/ho2smonitor.htm on the OBD in detail section. This explaines the function of the HO2S sensors.
Before you change them, you need to take a scan to make sure it is not the fuelling at fault rather than the sensors - if the fuelling is wrong then the HO2S sensors will not 'switch' even though there is nothing wrong with them.
Both of these DTCs indicate a high voltage for the HO2S sensors on both banks of your 24V, so it is not likely to be a connector fault (because this would normally show a low voltage rather than high.
Do another scan when the engine is hot, selecting MAF, RPM, HO2S11, and 21 and LTFT1 and LTFT2. Then let the scan continue for a while, drive it round the block perhaps, then stop the scan, save the file and play it back. Graph the sensors and check whether then go above 1v - if they do then they are probably faulty. Check both the Long Term Fuel Trims. If they are very low then they indicate that the mixture is too rich or the MAF is faulty. You could zip the three scans together and put it up on the anyboard site so we can have a look at it. ;D
These DTCs are often caused by something other than HO2S sensors, so do check this before getting new ones. ;)