Mercedes-Benz Sprinter Limp Mode Problem

Hello good people,
I am writing with confidence that my vehicle problems will be solved here.
A Mercedes-Benz sprinter 2007 Turbo engine with a driveability problem. Vehicle refused to drive above 50-60km/hr.
There are two trouble areas I need your expert help on

1. MAF and IAT circuit open
2. Glow plug module was burnt and a used one was bought as a replacement. I am still having the heater light on my dashboard and a flashing check engine light. I have replaced 2 glow plugs that were leaking diesel and also the broken fuel return line.

I have attached the DTC codes, but the Cylinder 1 injector circuit problem is not showing again.

I noticed the wire harness to the MAF And IAT looks abused and also a missing plastic. I have checked for constant current to the MAF and got 4v at first attempt and later 15v at subsequent attempts, and the mass of air is 289.5grams at idle. What could be the cause of a flashing check engine light?

Please experts in the house help your boy out.

Hello,
Anyone willing to point me in the right direction would be so appreciated.

Start by testing wires to maf sensor voltages plugged and unplugged of each pin at maf sensor then back probe connector at pcm for those same wires and see if voltages match. If they do I would say maf sensor is toast because 289 grams per sec at idle is way to much.

Thanks for your help

I’ve done the checks and results below

MAF 4 wire sensor

Checked all wires coming from the ECU with the MAF unplugged
5v reference wire gave 6.96v
Sensor ground wire (0.01v)
Constant ground wire (0.00v)
12v battery wire gave 17.5v

Checked all wires coming from the ECU with the MAF plugged
5v reference wire keeps dropping voltage to 0.58v everytime I plug it in the MAF (I installed a back probe pin, and the voltage goes back to 6.96v when I unplugged the MAF
Sensor ground wire (0.01v) plugged and unplugged
Constant ground wire (0.00v) plugged and unplugged
12v battery wire remains 17.5v plugged and unplugged

Since I’m getting IAT code also, I ran the test on the 3 IAT wires
5v reference wire for IAT plugged and unplugged remains the same 6.96v
Sensor ground wire (0.01v)
Constant ground wire (0.00v)

When I got this truck, the previous owner looped 3 wires from the fuse box area I suppose up to the neck of the MAF wires.
This means they’ve been trying to deal with the MAF issue

I’ve taken out the MAF sensor and I can’t find anything written on it and this makes me believe they must have replaced the MAF sensor with a Chinese knock off

A good MAF should have Bosch and the part number written on it I believe
I have the OEM part number (A0000943248)

Can I conclude the truck’s fault is a wrong MAF and not some wiring or ECU problem, and just go ahead to order the right MAF?

We're these measurements taken with engine running or just key in on position engine off?

Measurements were taken with the KEY in ON position and engine off

These voltages are too high.

What happens if you do a ground to ground voltage loss meassurement while the engine is running?

Preferably a test light on those grounds but try the DMM first.

Make sure every cicuit you test is backprobed while plugged in to get current flowing.

I have to agree with Bjorn on this voltage key on engine off should be 13 volts or less key on engine off.

Thanks guys.

So I decided to conduct the previous tests I did on my toyota car and these are the results
Test conducted on a 5 wire MAF/IAT sensor (Toyota Avensis Verso)

I had voltage readings on just two wires and other wires reported 0 volt

One wire had 17.04 volts plugged and unplugged engine off KEY ON. I remember I used my DMM to check on battery voltage on the toyota the day I ran the truck test and it was around 18volts

Another wire read 6.85 volts unplugged engine off KEY ON, then dropped down to 2.45 volts when harness wire is plugged into the MAF engine off KEY ON.

These tests 100% replicated what the truck is doing also.

I was watching scannerdanner video with his son on voltage drop vs resistance testing (flow charts suck)
Correct me if I’m wrong, the take away from that video is that voltage test on a ground wire is far better than ohms resistance test?

I have a DMM and a test light, how exactly do I conduct a ground to ground voltage drop test
What ground to ground am I testing ..... sensor ground, computer ground or battery ground

A YouTube video will suffice so I don’t fry my ECU

These are my 3 problem areas, could anyone determine the main culprit

1. A bad ECU ground due to rust and corrosion. I will snap a cable that broke off the truck engine block, but then it isn’t the ground bolt but just the plastic casing or strap that broke off from the engine block, can this ever affect my ground?

2. A short to ground of MAF sensor 5v reference wire

3. A bad MAF sensor shorting itself

All the technicians where I live lack the capacity to fix this problem, so I hope I can get all the help I need here.

Warm regards

The tests done so far on the 4 wire MAF sensor of the Mercedes Benz sprinter truck

DMM negative lead on battery negative terminal, then DMM positive lead on engine block (0.00v)
DMM positive lead on battery positive terminal, DMM negative lead on engine block (18v same as battery voltage)

>>>>Constant ground wire backprobed
Key ON engine OFF : 0.01v
Engine ON under load : 0.01v to 0.02v

>>>>Sensor ground wire backprobed
Key ON engine OFF: 0.60v
Engine ON under load: 0.59v

Looks like problem is on MAF sensor ground wire


IAT READINGS

WIRE ONE: 7.04v (same reading Key ON engine OFF/Engine ON under load) Backprobed
WIRE TWO: 5.29v (same reading Key ON engine OFF/Engine ON under load) backprobed
WIRE THREE: 0.02v Key ON Engine OFF, 0.01v Engine ON under load backprobed

DTC’s
P0110 IAT
P0100 MAF
P0101 MAF

MAF sensor reading doesn’t move an inch on the OBD2 scanner, it’s stuck at around 289.50 grams/sec even at higher RPM

I hope I can get directions with all the tests done so far
Warm regards

Given the voltage measurements on two vehicles with the digital multimeter reading 17 volts I think your dmm is faulty your obd reader says 12 volts in the photo so I would say that your MAF sensor is/has failed. Otherwise to be certain use another multimeter to do the checks again.

The big question is why am I getting DTC for IAT also. MAF and IAT are two separate sensors in the truck

@Bjorn
I believe my sensor ground wire plugged and unplugged should read around 100mv
Mine is reading around 600mv plugged and unplugged

Can I conclude that the problem is a sensor ground wire problem caused by a poor ECU ground
Also can you explain why I am getting an IAT DTC code.

Even though my sensor ground voltage is too high, does that stop the MAF sensor from functioning?

I have no idea if my MAF is digital or analog, but it has 2 grounds (MAF constant ground and a PCM ground). The MAF constant ground looks good but the PCM ground looks dodgy at 600mv
In one of scannerdanner chapters, he said the PCM gets its ground through the :MAF sensor. So this means a sensor ground problem is caused by the MAF and not the PCM?

Thanks hardtopdr2, I will try and get another DMM to do all these tests again

Hope to hear from you soon

babajis2010 wrote:

@Bjorn
I believe my sensor ground wire plugged and unplugged should read around 100mv
Mine is reading around 600mv plugged and unplugged

Can I conclude that the problem is a sensor ground wire problem caused by a poor ECU ground
Also can you explain why I am getting an IAT DTC code.

Even though my sensor ground voltage is too high, does that stop the MAF sensor from functioning?

I have no idea if my MAF is digital or analog, but it has 2 grounds (MAF constant ground and a PCM ground). The MAF constant ground looks good but the PCM ground looks dodgy at 600mv
In one of scannerdanner chapters, he said the PCM gets its ground through the :MAF sensor. So this means a sensor ground problem is caused by the MAF and not the PCM?

Thanks hardtopdr2, I will try and get another DMM to do all these tests again

Hope to hear from you soon

If you get 600mv on a ground wire that is too much yes. 100mv i max with loaded circuit.
It seems you have a bad ground for the PCM, one thing you can do really fast is backprobe one of the ground connections on the ECU and put the other end straight to ground. If that is done correctly you should have a good ground.
I am positive that would solve atleast some of theese problems.

I have not looked at the schematics for this car, but sensor grounds are shared, it might be that the IAT also has a bad sensor ground.
I would highly reccomend trying a known good DMM, because the readings youre getting on your DMM seems way off IMO.

So do the meassurements with another DMM if you can, then supply external good ground to the ECU. Or check for bad grounds on the PCM.

Let me know how it goes!

Summary of my test using a working DMM
Battery voltage 12.6v

Sensor 5v reference and sensor ground reading same thing

Breakdown below

UNPLUGGED MAF connector key on engine off

Pin (4) 5v. —-> this is the reference wire
Pin (3) 4.99v —-> sensor ground wire
Pin(2) bat gnd 0.01v
Pin(1) bat voltage 12.58v

PLUGGED MAF sensor connector key on engine running

Pin(4) 0.4v —-> reference wire
Pin(3) 0.4v —-> sensor ground wire
Pin(2) 0.01v bat ground wire
Pin(1) 14v battery voltage

What situation am I dealing with here please?

babajis2010 wrote:

Summary of my test using a working DMM
Battery voltage 12.6v

Sensor 5v reference and sensor ground reading same thing


PLUGGED MAF sensor connector key on engine running

Pin(4) 0.4v —-> reference wire
Pin(3) 0.4v —-> sensor ground wire
Pin(2) 0.01v bat ground wire
Pin(1) 14v battery voltage

What situation am I dealing with here please?

Still a voltage drop of 400mv on sensor ground.

Did you do any of the "tips" i mentioned?
adding an external ground or cleaning the ground points for the ECU?

He’s Bjorn

I’ve backprobed all the three brown ground wires at the back of the ECU connector and grounded them individually to engine block and I still have 4.99v at MAF connector sensor ground

A technician has also helped me to check for wire integrity between the 5v reference and also sensor ground

He put a jumper wire between 5v and sensor ground at the MAF connector unplugged and used a test light and blade to check each wire towards the end of the ECU and the tester didn’t light up for the sensor ground wire but lit up for the 5v wire. Which means the wires are not bridged according to him, if they did the tester will light up for both wires. He says it’s not a wire harness problem and probably from the ECU

I know scannerdanner said the ECU has a 5v regulator which may be shorted to ground in some cases.

No idea which step I’m taking next

I also checked all the three brown ground wires and all came with 0.00v

Did some homework and the part you think is the iat is not an iat. The iat should have two wires

At pcm 96 pin connector....
Pin 28 at pcm brown/dark green iat ground
Pin 84 at pcm dark green/white iat signal

I'll put a few pics up in a minute

Apparently your maf sends a temp signal back to pcm as well.

The truck is a Mercedes Benz

I know the dodge model has 2 wires to IAT.

That’s why I can’t use dodge wiring diagram to fix the Mercedes Benz

Attached pixs is where the IAT sits in the Mercedes’ Benz truck

Second pix is my truck with 3 wires
A 2007 Mercedes’ Benz sprinter 315 CDI
W906 OM 646.986