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Hide and seek

There are those who, instead of identifying and rectifying faults on cars, would rather change the vehicle’s capacity to detect such faults

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Published:  22 September, 2022

By Ryan Colley, Elite Automotive Diagnostics

Vehicles will always experience faults; It is inevitable. However, some choose not to repair the fault. They would rather play games by changing the ECM’s ability to detect the fault. Man-made faults are some of the most challenging to uncover, but with a logical approach and careful eye, these too can be fixed without too much difficulty. Following on from a recent article on how to determine whether software tampering has taken place, I would like to discuss the next case study.
This vehicle was brought to me by another garage after multiple attempts at repair. This included a replacement crankshaft sensor and donor ECM. The vehicle was a VW Scirocco 1.6 TDI (Engine code= CAYC).
I was informed by the garage that the vehicle only exhibits its symptoms, which are stalling and hunting, during acceleration. If the vehicle is left to idle it will be fine. First, I road-tested the vehicle and as the garage informed me, the vehicle would cut out fiercely and stall. At other times, the engine would attempt to stall, but would continue to run if the vehicle was then stationary.
I connected the diagnostic equipment to the vehicle and retrieved the fault codes. After a full system scan was carried out, the only fault code stored in the engine computer was related to the crankshaft sensor signal being implausible. This would make sense considering the symptoms the vehicle is exhibiting.
I then carried out another road test monitoring the engine speed and camshaft speed data parameters via the scan tool. I found when the fault occurred, there was no fault exhibited in the data being displayed by the scan tool. However, the fault code relating to the crankshaft circuit kept returning.
Suspecting the scan data refresh rate was not fast enough to catch the fault during its occurrence, I decided to connect an oscilloscope directly to the crankshaft signal itself, to monitor the sensor's output back to the ECM. Another road test was carried out with the oscilloscope attached. Please refer to Fig.1. The capture demonstrates exactly where our fault lies.
At times, the crankshaft signal was sticking at 5V, thus informing the ECM the engine had stopped. This, in turn, caused the ECM to cease injector control. Remembering initially that the previous garage had already replaced the crankshaft sensor, it seemed odd for another to have failed in such a short time. Therefore, before condemning the sensor itself, we needed to verify both the 5V feed and ground supply was present during the fault occurrence.
Another road test was carried out. At this point I was connected to the 5V supply to the crank sensor and the signal wire itself. Please refer to Fig.2. When the fault occured with the crankshaft signal, the 5V supply was also dropping, thus causing our sensor to stop outputting. Without a good 5V supply and/or ground, the sensor could not operate correctly.
I had at this point confirmed that the vehicle was experiencing a 5V supply-related issue to this circuit. However, it seemed odd to me that the engine computer had not set codes for any other circuits, and only the crankshaft sensor. I then retrieved a wiring diagram and examined it to find many other devices shared the same 5V feed from the ECM:

  •  EGR valve feedback sensor
  •  Rail pressure sensor
  •  Intake flap motor position sensor
  •  Turbo wastegate position sensor

Please refer to Fig.3. Again, all shared this same 5V supply but none of them were reporting any faults.

After closer inspection, it was clear the EGR pipe on this vehicle had been completely removed and blanking plates had been installed in both the manifold and cylinder head, to stop any leaks. Please refer to Fig.4. This was an issue as the engine computer should be setting fault codes relating to the EGR valve system flow. These capabilities must have been deactivated for no other fault codes to be present in the engine ECU.
I then read the engine computer's flash file and studied it to not only find that the EGR valve had indeed been deleted, but multiple fault codes had also been removed relating to all the sensors which were connected to the 5V supply issue. By re-flashing the control module with the correct/original software, I then received fault codes for these sensors during a subsequent road test, confirming the fault occurrence.
Armed with the information that the EGR valve had been deleted, and permanent fault codes now present in the engine computer for the EGR valve control circuit open, I decided to carry out a visual inspection of the connector on the EGR valve. This component was one of the sensors to share the 5V supply.

Finding the root cause
As you can see from Fig.5, the connector was nowhere to be seen. However, if you look closely, you can see the harness was running down the back of the engine, above the driveshaft. Further inspection showed that the connector had been rubbing on the driveshaft and was intermittently shorting the 5V reference circuit to ground, causing the drop out in the 5V supply to all the related sensors.
A wiring repair, replacement pipe and EGR valve were installed, and this vehicle was then cured. The original EGR valve had seized, causing the engine management light to illuminate, but a poor attempt at repair led to a shorted 5v reference circuit.
Keeping your eyes open for anything that seems out of the ordinary, like a completely missing pipe for example, is a good indicator that software tampering has occurred. This is becoming more and more frequent, making the diagnosis a lot more difficult due to pieces of the puzzle being taken away.
If you are ever in doubt whether software tampering has occurred, having access to dealer equipment is advantageous in these circumstances; allowing us the ability to flash the correct/original files onto the computers so we can then continue with the diagnosis.

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