AFT_B009

internal fault in the control valve itself. As I wasn’t familiar with the engine, I had a visual inspection to see whether the turbo actuator was electric or was controlled by vacuum, on this engine the control actuator was an electric unit so the fault could indicate an issue with the unit itself internally. I decided again for this fault to use live data as a starting point to see if any data was available for the control unit. P0069 – Barometric pressure not plausible with boost pressure: This fault is logged when the ECU compares values from both sensors for plausibility and if either are out of spec the code will set. Once again live data to view both sensors reading was to be my first check to see if some direction could be gained. P0299 – Boost pressure low pressure: This fault is exactly as it states, the ECU isn’t seeing the correct pressure from the MAP sensor it should be. Using multiple inputs from other sensors the ECU knows how much pressure the turbocharger should be creating via the electric actuator and as it is not seeing what it should be the code is set. This code could be caused by the turbocharger itself being faulty, the electric actuator not working correctly or the MAP sensor not reporting the correct pressure back to the ECU. Again, live data would be my first port of call as I could look at possible causes of all four faults codes and there may be a common link causing all four. Live data With my list done and my plan ready to execute, I then went into live data to see what the ECU was seeing and gain information to plan my next step. I set up a custom list view and brought up my sensors in question. All MAF, MAP, BARO and Turbo actuator command data PIDs were displayed and reviewed to see if anything stood out. As in my previous articles, knowing what the numbers displayed mean is crucial as if you don’t know, how can you make an accurate diagnosis? So, to keep it very simple for the sake of the length of this article, for MAF I want to see 0 air flow ignition on, engine off which I will refer to as KOEO (key on, engine off) steady flow at idle and increasing flow in relation to engine speed and load. I won’t list numbers as every scan tool lists different air flow measurements but common ones you will see are grams per second (g/s) and kilogram per hour (kg/h). For BARO I want to see a steady 1 bar under all conditions, KOEO, engine running etc. The main reasons this sensor is fitted is so that the ECU knows the current atmospheric pressure for correct air/fuel mixture for emissions and for plausibility to make sure other sensors are operating correctly. As in the UK we live at near enough to 1 bar atmospheric pressure this sensor should be as close as possible. For MAP I want to see 1 bar KOEO (plausibility check), then a pressure rise along with engine speed and load. Again, this is where the ECU compares BARO and MAP to each other. If one isn’t correct, it will know and log the P0069 code. This is required as if one drifted out of calibration and read differently but still operated within tolerance, the ECU would determine it to be ok which could cause running issues but no faults to be stored. For turbo actuator command, I want to see some form of change in command to the turbo again under engine speed and load to make sure something is happening as if there is no movement the turbo will not create any boost pressure. Observing data, I found the MAF to be reading what I expected under all conditions, and the BARO was correct. However, the turbo actuator control was a fixed value, which is clearly wrong. Was this a turbo issue or something else? The final piece of the puzzle was the MAP reading and KOEO. I had 0 pressure, and knowing we should see 1 bar, I have direction on where to go. Increasing engine speed and load, the pressure did rise slightly but we clearly have an issue. Remember, there is also no turbo control but we have to consider that if the ECU cannot see boost pressure, as a failsafe it won’t actuate the turbo in case it over boosts and causes some form of damage. Again, this reinforces the importance of knowing system operation. MAP sensor test With all this data gathered, my next step was to test the MAP sensor. This sensor was new, and through questioning Gordon I learned it was a genuine part, so why didn’t it read correctly? Testing power supply and ground to the sensor, both were ok so onto testing the signal wire. The signal voltage in live data was available and was compared to actual data gently back probing the wire, after checking both they matched exactly. Using my sensor simulator, I applied a varying voltage down the signal wire which matched in live data, so what next? We have a genuine new sensor, good wiring and correct ECU operation it seems? At this point with limited tooling and having had a quick look, bearing in mind it has taken me longer to write the article thus far than actually carry out my testing, I asked permission to arrange to take the vehicle to the workshop to carry out further testing. With permission from Gordon, a few days later I nursed the poorly vehicle up to the workshop to continue fault finding his vehicle. Out of curiosity I had asked if the old MAP sensor had been kept, which it had, so I brought it with me to test to see if anything could be found. On 24 AFTERMARKET SEPTEMBER 2020 TECHNICAL Below: Fig.1 www.aftermarketonline.net

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