LMM Failure: No Power? Get Help Now!

Hello,

I'm having a problem with my Audi A4 (8E) 1.9 TDI (131 hp), manufactured in 2002.
This morning, I started my drive at -14°C, and everything seemed normal, well, except for the windshield .
After about 500 meters, I suddenly had no power. The car is still running, but with very little power.
Overtaking is no longer possible.
I then read the error memory.

1 Fault Found:
17552 - Mass Air Flow Sensor (G70): Open circuit or short circuit to ground.
P1144 - 35-00 - -

After that, I got a new LMM (Linear Motion Module) from a friendly source and installed it, but unfortunately, I'm still experiencing the same problem.
The cables on the plug seem to be okay.
I have measured the following values:
Car side connector:
1 = not connected
2 = infinite resistance.
3 = mass
4 = 800 R to ground.
5 = 10k by weight.
4 vs. 5 = 10k5

Pin 2 is likely the culprit.
I then cut the cable at pin 2, but the contact inside the connector seems to be okay.

Does anyone have any idea what it could be?

THX.

When it comes to the pin configuration, it can only be this connector.



Pin 2 is connected to +Ub, which will likely be the ignition voltage. Perform a voltage measurement at this pin with the ignition turned on...

Greetings, Cryonix.

hello, please check the following.

kl.2 to mass (should have battery voltage), kl.2 to kl.3 (should have battery voltage).
kl.4 to mass (should have 4.5-5.5 volts)
kl.4 to kl.3 (should have 4.5-5.5 volts)
If you don't reach these values, check the wiring from the connector to the control unit. However, please remember to disconnect the control unit (unplug the connector from the control unit) and then check the wires for continuity.

Connect the HFM connector, pins 1 and 2.
connector HFM, pin 3 to pin 49.
connector HFM size 4 to pin 30.
connector HFM, pin 5 to pin 68.

Then, please check each pin for short circuits to ground, as well as to the positive voltage, and check the wires for short circuits to each other.

When checking the wiring from the HFM (humidity sensor) connector to the control unit, you should measure approximately 1.5 ohms of resistance. In the event of a short circuit to ground, positive voltage, or between the wires themselves, you should measure an infinite resistance.

Okay, please check the voltage at terminals 3 and 5 on the connector while the engine is running and the HFM connector is plugged in. You should see approximately 1 to 2 volts. Then, briefly accelerate the engine, and the voltage should increase.

And then, please get in touch (this whole situation smells like a misunderstanding or conflict).

Hello,

I found the error, but I'm not allowed to say .
'I couldn't measure 12V at pin 2, and I thought there might be a broken wire or something similar.'
What really surprised me was that fuse number 32 (engine computer) was defective, which I still don't understand, because the car was still running with the defective fuse, and communication with VAG-COM was also possible. I replaced the fuse, reset the error codes, and now the car is working again.
When I worked with that old LMM (likely referring to a mass airflow meter), I sometimes encountered a short circuit (SC) between pin 2 and ground. I'm not entirely sure how that could happen.
'Ideally, a longitudinal regulator should be installed to power the mass flow meter, and it shouldn't be able to short to ground. I don't understand that. The 5V connection is actually only intended to provide a ratio-metric output voltage that is dependent on the internal microcontroller's analog reference, which is supplied with the internal 5V as a reference.'
Perhaps this will be helpful to someone in the future, so they can also check this.

Thank you.

See? It works.

I hope you were able to make use of my little guide.
I'm always happy to help if you have any questions.

Best regards.

I will continue to rely on you/him/her/them in the future .
But to be honest, the technical article about it helped me a lot.

Okay, now I have to turn to you again with complete trust.
It worked well this time, but now the fuse has blown again after only one day.
Does anyone have the wiring diagrams for the Audi A4 (8E)?
It's fuse 31, I must have been mistaken about fuse 32.
After I replaced them, everything went back to normal.
I'd like to know what all is connected to the fuse so I can understand what might be defective, as it seems to be a sporadic short circuit.

THX.

It smells like there's a short circuit somewhere. Please check the wiring as I described to you.
Regarding your question, there are many things that could be involved, such as the mass airflow sensor, the boost pressure control valve, the EGR control valve, the heater relay for a large heating current, and in some models, the in-tank fuel pump. Also, check the 109 relay, or open it up and inspect the solder joints.
But first, please check your connections as I wrote to you.

Best regards, and please let me know as soon as you find something.

I will do it tomorrow.
Where is relay 109, and what is its purpose?
It's also not easy to measure because the error doesn't always occur, and right now, the fuse has tripped again.
I think one possibility might be the reversing light, but that's not working either. Perhaps it's the cable in the trunk; the mechanical stress on the cable might be a factor.
What do you think about me supplying the mass airflow sensor (MAF) with its own voltage first? But then, the exhaust gas recirculation (EGR) and the wastegate control valve would still be without power. I really think this is a difficult problem to diagnose. I'm not entirely sure yet, but a possible connection might be the reverse lights; I think the fuse might blow when I reverse, but I can't be certain yet, it just occurred to me.
I think a lot of work awaits me.

Does anyone have a wiring diagram? I think that would really help with identifying the wire colors and terminal labels.

hello,
'Today, everything was going well until I was driving home from work. I heard a fuse blow, and it seemed like there was a constant short circuit. Even a new fuse blew out immediately.'
Once I got home, everything was fine again, and I couldn't measure anything unusual.
The wiring from the mass airflow sensor (MAF) is fine, as it should be. At the moment when the fuse blows, no error can be detected.
The LMM cables are also compatible with each other.
In my opinion, the LMM is not necessarily the culprit, but I cannot completely rule it out.
I'm not really sure how to find the fault, as it doesn't always occur. In my opinion, I should disconnect the circuit of fuse 31 and insert several fuses to determine where the short circuit (SC) is coming from, but that's not possible without a wiring diagram.
Perhaps I will have to order the circuit diagram from Erwin (siehe Fehlerdatenbank) after all.

While searching for a wiring diagram, I came across the following:
http://mitglied.lycos.de/vwpassatfahrer/
Although it's for a Passat, maybe it will help someone here .
It's not a direct copy of VW data and therefore appears to be permissible.
We will continue searching.

Please provide me with the exact vehicle data regarding the wiring diagrams and send them to my postbox.

Sure, here is the translation of the text from German to English:

'Hello'

Hello,

I drove all day today without any problems. Maybe the temperature is to blame? Perhaps the cables are stiff and rubbing?
The friendly mechanic around the corner said that there are relays located under the ECU, and I should check them for corrosion. However, I couldn't see any corrosion on them. Everything inside the water tank looks brand new.

Hello,

Now, I'm quite sure that the problem occurs when the temperature is below -5°C, but not otherwise.
I got the wiring diagrams from a Superb, but I'm not 100% sure if they are accurate, but it's better than having no diagrams at all.
Okay, first of all, a few words about the schematics. It's a disaster. If I were to submit a plan like that, I would be fired .
What I've found so far should be attached to the left mudguard and the reversing light.
A70 and D136 should be the names of the power supplies.
A70 = Positive connection (15A fuse 31 in the circuit breaker distribution line).
D136 Plus connection -2 (15A) in the engine compartment wiring harness.
On gasoline engines, there's another connector located on the ECU (apparently for the throttle body), but this is not present on the AWX diesel engine.

I'm going to test supplying the LMM (likely referring to a mass airflow sensor) and reversing lights separately today.
I already disconnected the F4 fuse for the reversing lights, but that didn't solve the problem either.

Can someone who has insight into Audi's plans confirm that nothing further depends on this?

Thank you.

Okay, so I installed a fuse holder today. I added an extra one, and connected it to the S31 fuse, which is now 40A. I also installed 3 more fuses.
Connect a 15A fuse to the old cable (black/blue) and a 7.5A fuse to the mass airflow sensor (MAF).
The 15A fuse has blown again; it's cold again. The mass airflow sensor (MAF) is still receiving power, and the car at least seems to be running normally .
The third one is intended for further troubleshooting, to supply suspicious strands with power and see which fuse blows.
I don't have a wiring diagram yet, but as far as I can see, both the oil level sensor and the S31 cable pass through a brown 10-pin connector in the water tank. Since the sensor hasn't been working for a few weeks, I suspect that the problem might not be the sensor itself, but something else related to it. I hope it won't be as cold anymore soon so I can take a closer look. Maybe I'll have found a wiring diagram by then, and hopefully, we can figure it out.