Mercedes-Benz Sprinter Limp Mode Problem

Is this a north america sprinter or a European sprinter. I know we have quite a few members in the UK and Europe. Just want to make sure

It’s European left hand drive

Something is totally off here, if you have a 4 wire MAF, where does the output signal go?
Do you have a vin for this car?
I can look up schematics

WDB9061351N307239

Appreciate your effort a lot

I have to admit, I'm not so sure what to expect anymore.
I don't know how a 4 wire MAF/IAT works, I'm used to 5 wires. I don't see how it can report both intake air temp and mass airflow with one signal wire.
If you have the sensor plugged in, key on engine not running.
Do you get the same measurements?

I'm still on the bad sensor ground for the ECU.
The 5vref and the sensor ground is shared so if there is a fault with the ECU/ground, you should see the same measurements on all circuits that share this 5v and sensor ground. You might want to check intake air, map sensor, camshaft, crank sensor and so on for 5vref and sensor grounds.

MAF is separated from IAT

MAF is 4 wires
Constant battery voltage
Constant ground
Sensor ground
Sensor 5v reference that also serves as the signal wire

IAT 3 wires
5v reference wire
Signal wire
Ground wire

Sensor ground on the IAT looks good at 0.01v

Sensor ground at MAF looks bad at 4.99v

A ground wire or signal wire that is shorted with for example a battery voltage wire will give 11-14v

In my case MAF sensor ground is showing the exact reading of MAF reference/signal 4.99v when unplugged and mimicked it also when plugged both showing 0.40v. This leaves me to believe my sensor ground is bridging with my reference/signal wire

Problem has to be either the harness or ECU

The 1million dollar question is will a bad ECU ground cause my sensor ground to mimick voltage reading of my reference wire?

Can you depin the connector for the MAF?
If you have the tools.

Would be interesting to see what's on that sensor ground pin with the wire disconnected.

And to your question, a bad ground can cause a multitude of problems, so I really don't want to rule anything out.

Actually I’ve changed the connector of the MAF and problem persist. I’m thinking if the 5v wire is short to sensor ground, then it’s voltage should drop to zero

What’s the best way to check wire harness integrity (sensor 5v wire and sensor ground wire)
What fuses can I check just to make sure?
Unplugged I am not experiencing any voltage drop on the 5v wire, but I have (5v) voltage on my ground wire.

How do I find this bias voltage on my sensor ground
Is there a possibility that my 5v reference Wire couldn’t find a proper sensor ground and that’s why my sensor ground wire is reading 5v?

I think you would have to disconnect the harness on both sides, apply 12v on one side and test light on the other to be sure the wires are okay.

Thanks Bjorn

As you earlier suggested I will continue to chase a bad computer ground

If you can help me with ECU ground wiring diagram. I believe this ECU has 3 grounds if I’m not mistaken

I’m particularly interested in a sensor ground socket which is where my problem is.

Much respect

Since I know the problem is between the wire harness and the ECU, I did a short to ground 5v reference/signal wire harness test at the connector of the MAF unplugged and also connector at ECU unplugged using a digital ohmmeter.

I set the meter to the highest @ 200million before I could get a reading. It was OL the whole time when I used lower figures.

Using 200million ohms as my baseline, positive lead of ohmmeter to the 5v reference/signal wire and negative lead to a metal on the engine block and I got 70ohms that steadily kept increasing to 96ohms and above. I believe this test is supposed to stay at OLM ohms if there is no short to ground in the 5v wire.

This leads me to believe I have a 5v reference wire short to sensor ground, but then I’m not experiencing any voltage drop on the 5v wire with the MAF sensor unplugged and it drops to 0.4v with the MAF plugged. Or a shorted sensor ground wire causing a 4.99v in the wire.

I’ve done many tests to check for a bad computer ground and can’t find any faults in that angle. As a matter of fact this ECU doesn’t have any grounds connected to engine block or chassis. I’ve traced the journey of the ECU (F) connector where the ECU power and grounds are, and they all go through a hole into the truck driver compartment where you have all the fuse boxes, unless the wires are grounded inside the truck and not in the engine bay.

As for the plastic holding a cable to the gear box that got broken, i’ve checked and it turned out the cable went to the alternator.

I did a voltage drop test on the three ground wires at the ECU connector with the connector connected to the ECU and engine running.
Using a DMM, negative lead to battery negative terminal, positive lead to the back probed ground pin at the ECU and the three grounds came back with 0.00v or 0.01v. Looks like the ECU grounds are fine.

Any more suggestions with what I’ve done so far. I’m checking one more place tomorrow which is the fuse box, and it’s stated that ECU fuse must be 5A in the fuse PDF wiring info.

N.B//// My MAF and IAT figures are FIXED high on the OBD2 readings.

Given the codes you have.... Have you checked the intake boot to turbo for cracks/ or if clamp is tight on induction side of turbo?

I see that some sprinters have a seal that goes around the turbo before the big hose goes in, but mine doesn’t have the seal

I bought the seal and the hose wouldn’t fit with the seal in place. The hose goes from the MAF downward to the turbo mouth

The clamp is very tight at the turbo side without the seal though. I still feel MAF and IAT should make some movement on the scan tool even if the turbo clamp is missing. Both are stuck at a fixed number with a flat line

My MAP sensor makes some movement even though not the best reading
103kpa to 125kpa from idle to WOT
My WOT stops at 3000RPM instead of 5000RPM

I will be happy if I can solve this bias voltage on my sensor ground wire

can you see if the sensor ground wire and 5vref wire can hold a current?
by applying a power source on one end and lightbulb on the other.

I think I did this test under load using a DMM

5v dropped to 0.4v
Ground also 0.4v

Ideally the 5v should drop to 2.53v with the MAF plugged engine on under load and ground should be 0.01v.

If I can get the sensor ground to be 0.01v and MAF under load still reads 0.4v, then I will just go ahead to change the MAF sensor

Unless you mean a different test

Hey guys

I have tested the truck with another ECU and I still have sensor ground as 4.99v

What should a sensor ground read when the connector is unplugged from the MAF key ON engine OFF?

Am I measuring the sensor ground wrongly by unplugging the MAF connector, since it’s the MAF providing the ground?

I need to know I’m carrying out this measurement correctly. There are no clear videos online on how to properly test the sensor ground. The sensor ground is different from the constant ground.

Any help on this please

The fix for these DTCs was a brand new OEM MAF sensor



Although I still have p0101 which could be due to a vacuum leak

Thanks guys
So much appreciation for this community as I have learnt a lot in some automotive repairs