In the workshop recently we were presented with a BMW 1 series 116 petrol E87 model with a complaint of a hesitation under load or what can be described as a miss fire !
As always I initially interrogated the DME module (engine ECU) for DTC’s. I was presented with multiple DTC’S, SEE FIG 1 and so initially I decided to carry out a basic visual examination of the ignition coils and spark plugs.
The plugs did show early signs of spark erosion or corona ringing and the coils did look a little tired. On the strength of my visual examination I advised the customer to replace the coils with brand new genuine coils and NGK plugs with the proviso that we would need to carry out extended tests after fitting the coils.
I took the time also to clean the throttle body and realign using Autologic and simultaneously reset and fuel trim adaptation values.
Once reassembled I took the vehicle for a quick test drive approximately 6 miles which delivered an acceptable level of performance and didn’t present any dtc’s.
So I took the decision to finish the bill which included 1 hour diagnostic time at £85 +vat/1 hour mechanical labour £65+vat and 4 new Coils £25 x 4 and 4 new NGK plugs at approx £6 each. Total bill £268+vat. I’m not afraid to admit I held a little reservation in my mind to wether we had correctly identified and fixed the problem so I warned the customer about the lack of hard evidence and the chance that there might be intermittent faults still present which haven’t occurred during our test procedure but reassured him that what we have done for the cost is good common sense and the right place to start.
After a brief explanation of my findings and showing the customer the suspected faulty ignition components visually he paid the bill shook my hand and left.
It wasn’t until 2 days later he came back with what can only be described as a disappointed look on his face when he turned to me and said its exactly the same.
Not surprised by this I said ok let’s take another look offering the first hour diagnostic free of charge.
This time there were no fault codes present in the DME module, so I pressed the customer for more information and asked him to carefully explain exactly what is happening and he explained that the car would suddenly loose power and jerk violently whilst accelerating. Curious I took the vehicle for an extended test drive whilst carefully examining live engine data especially miss fire detected or (engine roughness) and only after 15 miles of driving the vehicle would do exactly what he described but I noticed the DSC light flash on for a brief moment so quick in fact I almost missed it. Eventually the vehicle would act up upon request at a certain load point normally acceleration out of corners or roundabouts.
I turned my attention away from live engine data and miss fire detect and closely examined DSC live data. All most immediately I noticed discrepancies with the two rear wheel speed inputs.
I quickly returned to the workshop to carry out a thorough visual examination of both rear wheel speed input sensors and pickups. The rear DSC speed input is taken from a ring attached to the drive shafts. Nothing initially looked out of place but when I examined a little closer and span the shaft I noticed an egg shape due to corrosion underneath the pick up. The sensor was hidden out of sight behind the shaft but it was clear the physical phonic wheel ring was distorted which would of course cause an error in wheel speed input to DSC !! Once the drive shafts were removed the evidence was clear and concise, the distortion in the shaft had actually caused physical damage to the ABS sensor.
The customer again was advised and quoted for the replacement of both rear drive shafts and sensors. I invited the customer down to inspect our findings and almost unbelievably he mentioned that he’d seen he DSC warning light flash on before but had completely failed to mention it. I always like finishing using my favourite quotes so he’s another one. Its actually a Chinese proverb but hey. ‘half truth, is lie’.
I always question myself and our procedure always tweaking and trying to perfect our diagnostic methodology and strive to deliver the best possible service and value for money. On this occasion it was no different but the fact remains the customer spent in excess of £250 + vat on a repair which didn’t fix the problem. Who’s to blame ?? Did I drive the car far enough? did I question the customer enough/ should I have carefully interrogated other systems on board before blaming the coils?? These are the questions we must ask ourselves in order to hone our skills and level of professionalism. All what I have mentioned above is up to debate and I welcome healthy debate. Personally I think I got it spot on and wouldn’t change my approach next time.
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