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Matt
Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 21988
Experience:  BEng hons Mech engineering, in auto industry 22 years
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2002 c class cdi car is in limp mode after scan code po100.

Resolved Question:

2002 c class cdi car is in limp mode after scan code po100. Hot air map sensor coming up new part fitted still the same even after the code was taken out any ideas reg.stew.

Submitted: 3 years ago.
Category: Mercedes
Expert:  Matt replied 3 years ago.
Hello

OK if the MAF ( mass airflow sensor) has already been replaced I'd suggest carefully checking the state of the wiring back from the meter as a damaged wire or corroded connector can also result in a faulty signal back to the ECU

if any wire section feels hard then it may have shorted internally and will need cutting out and replacing

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Customer: replied 3 years ago.

Wiring all ok still in limp mode and scanned still coming up with hot film sensor weak signal what does the hot film mean?

Expert:  Matt replied 3 years ago.
Hello

thats the MAF ( Mass airflow sensor) which you siad you've already replaced

if you're confident the sensor is OK and the wiring is OK then this could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

If this is OK then the wiring loom resistance needs to be checked between the MAF and the ECU to double check that there's no short or broken wiring