The power of two

Frank Massey works on a Peugeot with no teeth and a BMW with no PCM

Published:  10 October, 2012

A couple of interesting jobs came through our doors this month that I thought would be a good basis for this month's article. The first car was a Peugeot 407 SE, with the FZH engine code. The initial problem was described as drivability hesitation, as well as a MIL lamp error. Our first step was to interrogate the fault code memory and this revealed a 'throttle position range' error as well as a CAN communication error between the PCM and body module.

We then cleaned the throttle body and reset the throttle adaptation, following which, all appeared to function normally. Communication between the problem modules did not present any functional problems, the CAN network waveform (telegram) did not show any distortion.

Using the Autologic serial platform we were able to activate the throttle body fully with no obvious defects and following a full brief with the customer we agreed that further use would show up any intermittent errors. Job done? Unfortunately not.

Gnashing of teeth

The following day saw further problems. DTC's indicted the same problems, 'throttle range & stop' not reached and a CAN comms error between the engine powertrain control module (PCM) and body module.

(figure 1)

Figure 3: The windshield gravity drains were severly block

No profile

(figure 2)

During our testing it was necessary to support the vehicle battery with the Fronius charger. After plugging in, we noted that during the process of battery support the CAN telegram returned to its natural profile and free of distortion.

Further conductance testing of the battery confirmed poor internal health. Following replacement all CAN comms errors were eliminated. This was more a common sense challenge rather than technical but it did show the necessity to ensure basic test procedures are followed. The next short story highlights both common sense, careful evaluation of serial data and basic observation.


Initially, this car had been booked in with a complaint of drivability errors that included stalling and an intermittent MIL lamp error. However, on the day of the booking the customer telephoned to advise us he would be delayed due to the vehicle breaking down in Manchester, 35 miles away. When it arrived via the AA, we elected to conduct a global vehicle scan via the Autologic platform. Our original thoughts based on a detailed description of known history focused on previous work carried out by an independent BMW garage and a dealership technician (but on his driveway!)

These related to replacing the timing chains, crank angle sensor, cam ID sensor, Vanos control solenoid, oil and filter. By now I guess you can see what's going on in my mind... the most worrying comment related to the reported condition of the oil filter, described as very badly contaminated!

The owner had been experiencing intermittent problems with the Vanos control. Due to the change in vehicle condition a global scan, whilst the customer was present, gave us the opportunity to scale the extent of the problem. A whole goody bag of errors were present but the most obvious common denominator was no Can communication between various modules and the engine PCM.

(figure 3)

Blocked drain

Further inspection revealed blocked drainage channels both in the PCM electronics housing and the chassis below. The entire engine bay was steam-cleaned prior to the PCM replacement. Fortunately, the Autologic platform enables us to not only programme the PCM but also carry out the latest CIP update. Job done? Well, not quite. The engine ran and there were no fault codes in the CAN network - but a final global quick test confirmed two remaining faults, the first was seat occupancy sensor circuit error and the second was a steering angle sensor implausible signal. This fault rendered steering stability inoperative.

Sorting it out made the customer £1,400 poorer. However, the real question is had the very recent and extensive work been carried out with more vigilance, all of this could have been avoided. The 'service' had been carried out a week earlier, incredibly, on the driveway by a dealership technician! This 'technician' had failed to replace the cabin filter which was totally blocked and somehow failed to notice the blocked drainage system.

The CBS service log indicated the oil condition at 0% and the cabin filter at 30%. It would be unprofessional of me to comment on the work done previously, but feel well justified in my comments as to what should have been done. Cheap work is easy but value for money comes at a price. If only more customers realised that.

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