Rover 45 out of ' character '

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Rover 45 out of ' character '

Post by Robski » Fri Nov 30, 2012 11:08 pm

Vehicle : Rover 45
Engine code : K16
Year : 2004
Symptom MIL illuminated no running issues.


This car came with the MIL (Malfunction Indicator Lamp) illuminated but no reports of any running issues.
The first action was to read the PCM (powertrain control module) for the stored code/s.

P0170 Fuel system adaptions out of range was the only DTC ( Diagnostic trouble code) stored.

The car was then road tested & live data was watched for any anomalies, one thing that stuck out was that the up-stream O2 sensor, with my foot hard to the floor on the throttle pedal, was hitting a clean 0V, the scan tool used was the Sykes ACR4/G2 pod, on return from road test i put a bit of a test plan together.

I started by checking the fuel pressure, which was on spec, one thing i noticed at this point was it was still on its original fuel filter, the car was on its second owner from new & had low milage for an MY 2004, so i replaced it as a matter of course.

Re-road testing after the filter change made no difference to the up-stream O2 sensor 0V reading, i contemplated checking fuel flow at this point but decided to hook the Pico up & see what’s occurring with the O2 signal, the reasoning for not checking fuel flow was the car never hesitated or exhibited any lack of fuel symptoms.

This was the first capture i took which shows the O2 sensor behaving normally.
Rover 45_O2 working normally.JPG
After this capture i then carried out a test forcing the O2 sensor lean & rich, this is when the fault showed up.
Rover 45_CSD_.jpg
It was clear now that i was looking at CSD (Characteristic Shift Down ).

Characteristic Shift Down.

An oxygen sensor compares the residual oxygen content to an ambient air reference, it does this through the sensors wires. If the sensor ceramic cracks and the exhaust gas gets through the crack the reference side gets contaminated, the oxygen sensor then will start to work in reverse because the reference side will have less oxygen than the exhaust side therefore generating voltage in the opposite direction. This is seen as a negative voltage. The sensor can still switch as the average voltage approaches zero and continue negative. This symptom can clear up on its own but if the ceramic is cracked the Characteristic Shift Down will no doubt return.


A new O2 sensor was fitted, the car was road tested & the O2 sensor behaved as normal hitting around 900 mV with the throttle on the floor.

Another case where the true real time data is seen by the Picoscope compared to live data from a scan tool, as simple as this study may read & the outcome turned out, the Picoscope really gives diagnostics another dimension & i wonder without one what the next step might have been ?

jon morgan
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Joined: Fri Nov 19, 2010 10:08 pm

Re: Rover 45 out of ' character '

Post by jon morgan » Sat Dec 01, 2012 2:55 pm

I like the explanation of CSD - it all becomes clear why I see that negative voltage on some O2 sensor tests.

Good diagnostics.

Darren Cotton
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Joined: Thu Jun 16, 2011 9:53 pm

Re: Rover 45 out of ' character '

Post by Darren Cotton » Sun Dec 02, 2012 3:03 pm

Good use of both, diag tool and scope. I have only experienced this CSD a handful of times, once on a shogun which using the same process of monitoring the live data and then carrying some simple tests with the scope it proved the O2 sensor was reporting incorrectly.

Its good to prove a fault with confidence and that the money you are spending is necessary , and your not just guessing.

maybe without the proof from the scope some would be playing parts darts...


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