Error code P0100

Sep 28, 2020
Hello All
Wondering if anyone out there has come across this issue, which I got on my 2009 Leon Cupra.
I have a light on the dash when I plug in my OBD reader it shows error code P0100 which relates to a Mass Air Flow sensor issue. I have replaced the MAF with a original sensor but the light is still coming on along with the same code. I'm going to replace the PCV valve next, but wonder if anyone else has had this problem and how it was overcome.
Thanks in advance


Active Member
Nov 19, 2019
Hello there,

I think the error code P0100 is circuit malfunction.

The error code you have is stating the electronic connection is lost or is out of OEM range.
Possibly is a wiring fault or a short circuit either in the connection plug itself, or the wiring loom somewhere between the ECU and the connection plug for your sensor.

You'll need to trace/follow where the air flow sensor wiring loom goes, look for any obvious signs of damage including the connection plug, or area's where the wiring loom has been rubbing against, if it looks ok then you'll need a multimeter set to 20volts, switch on your ignition and check you have power of 12volts at the connection plug to sensor, and check you have a good earth also.
Then with the connection plug reattached to sensor, you want to check you have the base line signal voltage, which is roughly 5volts + or - depending how much throttle is used.

12volts should be seen at the power wire.

Black or brown wire you should see a good earth when using the multimeter.

5volts should be seen with ignition on or at idle from the signal wire, which will fluctuate as you rev the engine.

If you don't see any reading from one of the wires when testing, then switch off engine including ignition, and you'll need to do a continuity test down the wire, you might have to do this in sections going down the wire, unless you have a wiring diagram to tell you which connection pins are for the air flow sensor on the ECU.

Regarding the continuity test with the multimeter, you should hear it bleep which conforms the wire is intact, be you'll need to check the whole wire/s that are found to be at fault, from the sensor to the ECU, any break in the wire or corrosion or any wire that is damaged and touching the body of car can result in the error code you have.

This is a thread I posted in recently about a similar error code as yours relating to the Mass Air Flow Sensor.
I put up details that might help checking the earth wire on the connection plug.

To be honest it wouldn't hurt checking the PCV valve, I've heard in rare cases it can sometimes bring on the error code/s P0100 or P0101, where the valve isn't working correctly causing the air to fuel ratio to be incorrectly read by the ECU.

Hope this helps
Last edited:
Sep 28, 2020
Thank you for your response, I have already ordered a PCV valve, which will be here this week, hoping that sort it.
If it doesn't I will follow your instructions and try to trace the fault.
Again thank you
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