A recent head scratcher presented to AECS Equipment Technical Support was a late model Holden Colorado diesel with P0335 and P0336 fault codes indicating crank/cam correlation issues....
Problem presented to the technical support team…
Late model Colorado with high mileage. Keeps coming up with P0335 and P0336 fault codes which bring on the engine check light. The vehicle runs fine.
The workshop had an ATS 6004XM 4 channel scope, so we suggested that they record the crank/cam sensors while driving the vehicle. This will allow us to see if the sensors are switching correctly and if there is any signal drop out or timing deviations between the sensors. ATS scope software can add a crankshaft angle measurement for every rotation of the crankshaft specifically to measure the correlation between the cam and crank. This can show up timing errors or variations from loose tensioners/chain/belt etc. The following recording was shared with the tech team.
In the scope recording below we can see the camshaft sensor recorded in the red trace and the crankshaft sensor recorded in the blue trace.
The red cam sensor signal is being switched from 5 volts to almost 0 volts when the hall effect cam sensor has one of the lobes on the camshaft pass the sensor's tip. This gives a square wave output to the engine control unit.
In the recording below we can see sections of the cam sensor signal when it is at 5 volts collapsing down towards 0 volts. Also in the 0 volt section there is collapsing down towards 0 volt ground. This is not a correct signal.
Thinking time
What could cause our signal to drop out like this ?
Loss of power supply - YES - Our supply is collapsing ie damaged wiring etc.
Loss of ground supply - NO - We can switch 5v to 0v so must have ground.
Sensor issue - YES - Could be internal break in sensor electronics
A new genuine sensor was fitted and the following recording was carried out with the new sensor installed.
Everything now looks in order with no drop out. Clean 5 volt and 0 volt square wave signal coming out from our sensor. Problem solved and out the Colorado goes.
But only to come back in 2 weeks time with the check engine light on again!
The same fault code and scope recording of the cam sensor were found.
Time to look closely at the vehicles wiring loom between controller and sensor.
If you disconnect the multi plug at the ECU and sensor, identify your wires, you can carry out insulation resistance tests using a megger ohm test meter. The meter will pump up the wire with a predetermined voltage on one probe, then run the other probe along wire to see if insulation is intact.
However, seeing that installing a new sensor prior gave temporary relief to our vehicle's problem, the technician did a quick visual check of the wiring around the sensor.
In the picture below you can see the diesel injector line has been giving the sensor wire a deep tissue massage. Note burning on the injector pipe. This is definitely what you would call being rubbed up the wrong way!
After repairing the wiring harness and securing it so it does not chaff again, the vehicle has gone out and not been back since for this issue.
Being able to see what is going on in wiring systems makes narrowing down likely causes a lot easier, directing your time/effort into procedures that are more likely to result in finding problems sooner.
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