17 Jul 2024
The voice of the independent garage sector

A month in the life of a vehicle technician

In this month’s article, I have chosen a very diverse collection of challenges presented to me, with a mixture of diagnostic problems and mechanical engineering issues. I am going to focus on the engineering issues later as I think they expose typical shortcomings seen in many garages, specifically with experience and engineering assets.  
    
My first story should shame us all with regards to garage ethics. I was asked to check an engine MIL light on a hybrid Honda. The extracted code suggested a bank 1 sensor 2 heater circuit error. I opted to raise the vehicle and examine and remove the offending sensor. Once raised it was clear the catalyst had been replaced with a straight length of pipe, removing the post cat sensor and tucking the open socket into a chassis lightning hole. Please refer to Fig.1.
    
When checking the vehicle records, I noted the catalyst had been removed and discarded with the sensor during a previous MOT test. As hybrid vehicles do not require an emissions test, a MOT pass certificate was able to be issued. I am not clear what implications the MIL lamp status would present during the test. The notes also indicated the customer could not afford the cost of a replacement catalyst.  Here is my take on this; We are not here to offer a financial lifeboat to vehicle owners. We are here to offer a professional, durable, and efficient repair service, at a cost. We should however also offer accurate technical advice as to cost value ratio.

Avenue of rectification
BMWs – I love them! Well, not really. A 320d that came into us failed its MOT for a nearside brake light failure. Initial examination exposed water ingress in the light cluster socket. Please refer to Fig.2. A replacement housing and socket with new pins duly arrived and was fitted. All lights except the brake light worked. Serial interrogation showed the maximum number of ignition cycles, which is 50 in case you were wondering, had been exceeded. Therefore, the voltage supply to the stop lamp is permanently interrupted. Please refer to Fig.3, showing BMW serial data.
    
Initial research suggested a new footwell module was required. However, further research uncovered that it was possible to access the lines of code and reset the ignition cycle count registry. This demonstration was not using an OEM service tool. As I was on holiday I am not sure what further steps were taken to explore this avenue of rectification. I do know we did replace the module and perform a repair. There are so many fuse and relay panels on BMWs, so why not have one for lights? Answer me that, Munich.

Simple things
Next, a Land Rover Discovery – I love these as well! This one came as a non-run vehicle. “Why?” I hear you say. Well, apparently, a low SCR additive warning had surpassed the final warning status. Serial data appeared to indicate the additive tank was overfilled. The filler is under the bonnet, with the tank located at the nearside rear, adjacent to the wheel arch. Once the hard-shell cover is removed, a drain gland allows easy draining. Not so fast, three simple things to do. First, smell it; It should be odourless, with a SG of 32.5%. Next, check the quantity. Finally discard it and refill with new urea. As I recall, the capacity is 14.5 litres. Using our serial tool reset, all the adaptive values enabled the engine to run. However, several adaptive values could not be accessed due to the following DTCs:
 

  • P2BAE-00 NOX EXCEEDED
  • P2BAF-00 NOX DRIVER INDUCEMENT ACTIVE
  • U029E-87  LOST COMMS NOX SENSOR 2
  • U0001-86 HIGH SPEED CAN COMMS BUS ERROR.


A new sensor had been previously fitted, so came my Pico to check CAN high/low, with confirmed distortion and a strange voltage pull up to around the 8-volt range. Checking the wiring codes to the sensor, all colours matched factory spec, which means they are incorrect. Why? The replacement OEM Bosch sensor had also been modified, which required a wiring modification. Please refer to Fig.4.

  •  C1 WHITE/BLUE +12v
  •  C2 VIOLET CAN H
  •  C3 VIOLET /WHITE CAN L
  •  C4 BLACK GROUND
  •  C5 X


Once corrected CAN was restored, all DTCs cleared and all adaptive procedures were carried out.  Please refer to Fig.5, showing the Pico CAN waveform.

Engineering tasks
Finally, some engineering tasks. Two consecutive days saw broken injector bolts come into the workshop, I suspect due to using power tools and not applying a more controlled smooth torque via a hand ratchet. The first had broken the bolt and striped the thread in the process. The break was flush with the top face so cantering a drill was not a problem. The bolt core came out relatively easily with an easy out. The next task was fitting an 8mm helicoil, in fact I fitted two due to the length of thread on the clamp bolt .Please refer to Fig.6, showing the helicoil kit.
    
The second breakage was not so simple; The clamp bolt had sheared 20mm down the bore. Centring the drill was going to be very risky. Not a problem with the head off using a pedestal drill. By a lucky twist of fate there was a 9mm counter bore before the 8×1.25 mm thread. I elected to manufacture a drill guide tool, 15mm into and 15mm above the hole. A 6mm centre allowed me to confidently centre drill the bolt in situ.


This is where engineering infrastructure and experience comes in. The broken bolt was so hard none of the available drills would cut. I have previously explained that my main toolbox is at home, and for good reason, so I had to select a cobalt drill from my personal drill set. There are several ways to identify a cobalt drill. For one thing, the shank will carry the abbreviation CO. Alternatively the cutting head may, but not always, have multiple cutting angles. Normally 5%-8% cobalt.
    
Do not use a cutting lubricant with a relatively high cutting speed. Knife through butter came to mind as the 6mm centre drill went down the bolt perfectly. The tapping drill for 8mm is 6.8mm so a conservative 7mm drill would help clear the old thread swarf from the bore. Using first, second, and plug taps restored the original thread, due to the depth of the thread. It was necessary to raise the taps to clear the flute of swarf and residual debris from the thread bore.
    
This type of repair is never a race against time. A new head casting was £2,500 plus labour.  I don’t know what the customer was charged I would value the task at £400-£500, half a day’s labour.