L322 Vogue 2006 4.4 V8 MAF/limp mode issues

Hi everyone - looking at a friend's 2006 4.4 V8 Vogue RR which has just started going straight into limp mode (2200rpm max) from startup. iCarsoft CR MAX shows P0102-00 MAF low input and P0121 Throttle pedal position sensor A circuit range performance. Also the Live Data display shows a constant 0v on the MAF output (presumably going back to the ECM?). I have cleaned the MAF, replaced throttle body and removed and tested the throttle pedal assembly on the bench with an external 5v - all good and no change.

My question is - is the actual MAF fed with both 5v and 12v? The description in RAVE infers that it is and the wiring diagrams show that it should be also. However, I am not getting the 12v feed on the 5 pin plug that plugs into the MAF - only 5v and three grounds. There are 5 wires which again corresponds with the wiring diagram. It looks as if the 12v comes from a fuse and is shared with other devices.

All I really need to know (to be able to continue this train of investigation) is does this particular setup require the 12v and if it wasn't there, could that be my problem. If anyone had the same vehicle, it would be great if they could confirm that there is 12v on pin 1 and 5v on pin 5 with the ignition on and the MAF unplugged.

Many thanks all....Peter

If the wiring diagram shows a 12 volt feed to the MAF, you can be pretty certain that if the 12 volt feed is missing the MAF will not be working.

Datatek said:

If the wiring diagram shows a 12 volt feed to the MAF, you can be pretty certain that if the 12 volt feed is missing the MAF will not be working.

Click to expand...

Thanks for responding Datatek - yes, appreciated. Just that I could find no online comments regarding this and wanted to confirm before I start looking at the loom and interconnections. Never thought the MAF sensor would need two supplies - part of the wiring diagram from RAVE attached here showing the 12v feed with the 5v coming from the ECM.

The 12V is for the heating of the hot film element, the 5V is for the temperature measurement sensor. As a general guide, actuators require battery voltage - even solid state ones, whereas sensors require 5V.

Ah - thank you. Will start searching for the lost 12v…

Personally I'd start by finding the splice - if nothing else, you'll have a good point to run an overlay wire into the harness.

Sorted - blown 15A fuse in Engine Fuse Box - moral: check the obvious first. !2v on pin 1 of the MAF sensor now restored - engine running normally. Don't know why the fuse blew but it looked original so maybe just tired and worn out (like us all).
Thanks for the comments people...

According to your schematic, it should be a 30A fuse...

Yes - however, I'm not sure if the diagram I uploaded is the correct one for this vehicle - it should be as is supposed to be for a 4.4 V8 from my RAVE. The additional diagrams (in three parts as below) are what I originally found and this shows fuse F7E 15A feeding via two interconnectors pin 1 on the MAF. I can confirm that it was an original 15A fuse that had blown and that there is now 12v on MAF pin 1. The 12v fed from the 30A fuse in the original diagram I posted shows as going to pin 2 of the MAF - not pin 1. It looks as if this vehicle's wiring matches the diagrams included here not what I originally posted. Sorry about the image quality. Now done a few miles on the road and all working correctly once codes cleared.

Have just realised that the differences maybe between diagrams for the BMW and Jag engines - not sure which this was - the MAF is at the front right corner of the engine, not left front as seems to be in the BMW images I've found online. Anyway, done and working.