Advice Re. 2.0TDI Ultra with P0101 MAF and P0111 IAT Errors Please

[WiteWulf]

Hi folks, I'm new here, so hello!

I recently acquired a 2014 A6 Avant C7 SE Ultra 2.0TDI (140kW/190HP). The car has 166k on the clock, but the previous owner destroyed the engine (cheap timing belt failed, valves met cylinders) and I bought it from a relative's garage that had fitted a second hand engine with 52k on it. New timing belt, pulleys, tensioner and water pump were fitted at the same time. The car exhibited a number of Exhaust Gas Recirculation (EGR) problems after the replacement engine was fitted, but these were resolved before I bought it.

The car runs very smoothly, with no reoccurrence of the EGR problems, but I have frequent and easily reproducible P0101 MAF (Mass Air Flow) and P0111 IAT (Intake Air Temperature) range/performance errors.

I drive relatively sedately, but when accelerating away from traffic lights, or up a motorway slip road or hill for more than 5 seconds or so, I'll often get the flashing glow plug lamp on the dash (which disables the auto stop start). I may be imagining it, but it seems more frequent in colder weather. This will clear after stopping and restarting the engine. Reading off error codes with Torque Pro and an OBD interface shows nothing after this has happened.

Less often I will get the engine warning lamp lit (almost always after a flashing glow plug lamp, but once without). This does not clear after an engine restart, and reading off error codes gives one or both of:
P0101 - Mass or Volume Air Flow circuit range/performance error
P0111 - Intake Air Temperature range/performance error

I am able to clear these codes with Torque Pro and the car never seems to go into limp home mode, for what it's worth.

NB. the MAF sensor was replaced as part of the work to resolve the EGR problems (high and low pressure EGR valves also replaced, not cleaned).

There errors seem to be relatively common on Audi owner forums, but I wondered if, with the additional information given above, someone might be able to offer advice on this specific case?

Some posts seem to suggest that IAT sensing is a function of the MAF sensor on these engines, while others state that it's a separate sensor, or in one of the MAP sensors. School physics tells me that temperature and pressure are linked; if the engine is getting an incorrect air temperature reading this could throw the pressure reading/calculations out of whack. With my symptoms seeming to occur more frequently on cold mornings, could this be linked?

There are also a high number of threads with people failing to locate the MAP sensor. Some models of car appear to have more than one. I've located a boost/MAP sensor mounted on a bracket above and to the rear of the engine (part number 04L 145 049 F). Is this the one involved in these errors?

[Crasher]

My immediate thought is aftermarket Air Mass Meter. The intake temp sender is in the AMM and the charge air temperature sensor in the combined MAP THRUST sensor. What is the VIN and the details of the AMM fitted?

[WiteWulf]

Thanks for taking the time to look into this fella, appreciated.

VIN is: WAUZZZ4G4EN173360

The MAF sensor currently in place is a Hella unit, part no. 8ET 009 149 44

spareto lists this as compatible with Audi part "03L 906 461 A", and appropriate for use in this model of engine (2.0 TDI 140kW/190HP).



Also, I did 200 miles up and down the M1 at the weekend without any problems. First thing this morning, in the 2degC weather, the engine warning light came on almost as soon as I set off, doing <30mph up my street.

I popped the OBD reader on it when I got to work 15mins later and it was another P0111 Inlet Air Temperature out of range error. I had a dig around in Torque Pro and found that it will report live data from the IAT, so I had a look and it was reading 82degC, which didn't look right. I'd expect it to be close to ambient, right?

I cleared off the P0111 error again and left it. A few hours later I came back to the car and, with the engine stopped, the IAT was still reading 82degC. I took it for a quick spin up and down the M1 and it never moved off 82degC, so it looks the inlet air temp sensor is faulty. To confirm my cheapo eBay bluetooth OBD reader was sending live data I was also displaying MAF and CACT values, which fluctuated according to me accelerating and backing off.

[WiteWulf]

I had time to do a bit more diagnosis today.

I took the MAF sensor off and confirmed it was very clean inside, and noted a new air filter while I was at it.

With my multimeter on the 4-pin multiplug (disconnected from the MAF sensor) I was able to establish 12V on pin 1 and GND on pin 2.

I cleaned the loom multiplug and socket on the MAF sensor with contact cleaner (being very careful not to get any inside the MAF sensor) and reinstalled the MAF sensor.

Running the engine with the MAF sensor reinstalled I again noted sensible values that reacted to throttle activity for MAF, but IAT remained stuck at 82degC.

Removing the multiplug again with the engine running I immediately observed the MAF drop to zero g/s and IAT go straight to negative 40degC.

So, it looks like the temperature sensor in the MAF sensor is sending bad values, would you agree @Crasher?

[Crasher]

Sounds plausible.

[WiteWulf]

Thanks. I'll get it replaced (the MAF sensor) under warranty and update the thread with results.

As an aside, through the warm weather of the last few days, I haven't had a single error from it, and I've deliberately been booting it when I get the opportunity.

[WiteWulf]

While waiting to get the new MAF sensor, I did some more testing based on the MAF, MAP and CACT sensors all apparently running off the same power rail. I've read elsewhere that one of those sensors being faulty can manifest as problems in the other sensors (although the readings from those sensors looked fine).

With this in mind, I disconnected the MAP and CACT sensors one by one and observed no change in the temperature values being output from the MAF/IAT sensor.

It's looking more and more like the MAF/IAT sensor is faulty, as initially identified by Crasher. I'll hopefully get that swapped out soon.

[WiteWulf]

I just got the replacement MAF (a Bosch one this time) and it's reporting a sensible IAT value straight away (matching the ambient).

Either the Hella one was incompatible or faulty, we'll never know, but this appears to have sorted it. I took it for a quick blast up the motorway, flooring it when I got the chance (which was always likely to throw an error) and it didn't miss a beat. That said, it's a warm day, the warmest it's been since I've had the car (and the problems), so a true test will be when it's cold again, I guess.

Thanks for the help diagnosing this.

[Crasher]

Chinese Replacement Auto Parts

[WiteWulf]

Quick update on this one:
Since replacing the MAF sensor I'm no longer getting the P0101 and P0111 (pressure and temperature errors), so that's good, but I'm still get the odd flashing coil lamp and P0402 EGR excessive flow error when accelerating hard.

I'd read that these can often be caused by a bad MAF, but as I'm still getting them after replacing it there must be another problem elsewhere. I just wanted to make it clear for anyone reading the thread that replacing the MAF sensor has *not* solved the P0402 EGR issues.

I'll keep on investigating, and report back if I figure it out.

Here's VCDS output, if anyone's interested:

1 Fault Found:
25221 - EGR System
P0402 00 [096] - Excessive Flow
Intermittent - Not Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 5
Mileage: 270936 km
Date: 2025.03.26
Time: 21:10:26

Engine RPM: 2346.00 /min
Normed load value: 69.8 %
Vehicle speed: 114 km/h
Coolant temperature: 57 °C
Intake air temperature: 106 °C
Ambient air pressure: 1010 mbar
Voltage terminal 30: 14.480 V
Unlearning counter according OBD: 38
EGR travel diagnosis: strongly increased NOx emission: 59.4 kg/h
Exhaust recirc.valve 1 bank 1: posit.feedback - Actual value: 0.02 %
EGR travel diagnosis: marginally increased NOx emission: 58.7 kg/h
Exhaust recirc.valve 2 bank 1: posit.feedback - Actual value: 0.00 %
Exh.recircul.valve 1 bank 1: pos.feedback - Actual value: 1.61 %
Pressure after throttle valve: calculated: 308.0 hPa
O2 sens. 1 bank 1 upstrm oxi cat: raw value: 1.3220