MAY 2024 AFTERMARKET 29 www.aftermarketonline.net prove the theory. Accessing the MAP sensor and checking the wiring with a multimeter showed 0 volts on what should be the 5v supply pin, confirming we had a circuit low fault as per the trouble code. The question now is whether it is a sensor shorted pulling it low, a wiring issue or possibly even an internal control module fault. Leaving the meter connector and going around the engine bay I decided first to disconnect each sensor one by one and see if any would bring our 5v back. When I disconnected the electronic turbo actuator the 5v returned. Reconnecting the MAP sensor and rechecking live data showed my numbers now to fall in line with where I would expect. Testing the wiring at the actuator showed everything to be as expected so I had a shorted turbo actuator. At this point I must add, as you can see in the pictures, this vehicle was presented with the bonnet missing. As it sat outside for months this way, I can only presume that the water had made its way into the turbo actuator and caused a short on the circuit board. Plausible feedback data I then decided to recheck the non-start complaint and the engine still would not start even though we now had plausible feedback data from the sensors, However, my temperature gauge would still go to maximum but I could communicate to the ECU so something was clearly amiss. After a few more checks I decided the next step was to check for technical service bulletins. As I know the JLR product well I remembered one that detailed very similar faults and showed steps to confirm the fault. Like I have always mentioned, a solid diagnostic process should include checking for technical bulletins along the way, I just had to re-read the bulletin to remind myself of the full details again. Concern Referring back to the bulletin it said a customer may report a concern that the starter motor rotates at normal cranking speed. However, the engine will not start and the instrument pack temperature gauge needle is in the red segment. During diagnosis DTC p068A-00 may be stored in the engine ECU. This matches our complaint and we also have this fault code stored. The bulletin explained the cause, which was that a small percentage of microprocessors in certain control units can lock up during data storage after engine shutdown which would then lead to a non-start on the following drive cycle. The bulletin showed a test sequence, then if all was ok to check the ECU build date and to compare to a table showing the faulty date range. Anything built before 14 October 2009 would be affected, but anything after this date would not apply and to carry on testing the vehicle. The bulletin said firstly to check a fuse that was taped to the wiring loom under the driver’s seat that was one of the main fuses for the engine ECU power supplies. Once switched, the main relay would supply 12v through this fuse and then splice into two wires to supply the control unit with two power supplies. The bulletin then said to check the bulkhead ground points for security and condition. Then if ok, test the main relay for correction operation which was also housed under the driver’s seat. Then you need to check and compare the dates on the ECU sticker to see if it was within the faulty age range, and if so replace the control unit. As the control unit on this vehicle was sitting loose and easy to access I had a look at the date and it was built in May 2008 using the date table. This put it squarely in the affected range but I first wanted to make sure we had the necessary power supplies and grounds and test what the bulletin had mentioned. Once I had removed the driver’s seat and access panel to reach the fuse box I was met with this. Please refer to Fig.4. At first, I wasn’t sure what relay this was but after checking against technical information this was the main relay I was going to be testing as part of my test plan. I think we can agree that this is not something the manufacturer has done. Comparing to the diagram again, I could see we should have two fuse-fed 12v supplies coming to relay terminals 30 and 85 on brown/light green wires which starts off as Fig. 3 Fig. 4
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