VW Passat 1.9 TDI: Error Codes G70, G81, G62

Hello everyone,

I hadn't been on this site for years, so I had forgotten my username. I've just registered again.

Regarding my issue:

Passat 35i, 1.9 TDI, 1Z engine.

After starting and driving, the engine exhibits poor performance and a high idle speed. Subsequently, it becomes difficult to start, and the glow plug indicator light remains on for approximately 10 seconds.

Error codes read with VCDS.

Lmm G70
Fuel temperature sensor G81.
Geber für Kühlmitteltemp. G62

Everything short-circuited to the positive terminal.

More G79.
And the brake pedal.

Implausible signal.

The error cannot be deleted.

My assumption is:

Control unit (unlikely).

Mass errors.

Visually, everything seems to be in order in the engine compartment.

Is there anyone here who has experienced a similar problem before?


Best regards from the beautiful Lahn Valley.

Marco.

Attached is a recording of the VCDS scan.

Hello,

It would be helpful if you could include an Autoscan.

That makes dealing with the large number of errors much easier.

What have you checked so far?

Are the fuses okay?

Were actuator tests performed on the individual components?

Wiring checked?

Checked the connectors for corrosion?

If the brake light switch and the lamp are working correctly, then the wiring harness in the area of the tailgate likely has a broken wire. A common consequence of this is a blown fuse. Alternatively, the connector may be corroded.

The LMM (lambda-controlled mass airflow sensor) may be responsible for the poor performance, and the coolant temperature sensor may be responsible for the increased idle speed.


Best regards,

Michael.

Hello Michael,

I'd be happy to do an Autoscan tomorrow, but does it even work on older VW models?

Fuses are all okay. Brake light switch is okay.

Surprisingly, the error appeared for the first time yesterday and seemingly out of nowhere.

Therefore, I don't believe that various sensors, including the mass airflow sensor, all failed simultaneously.

The brake lights are working.

I suspect a broken or faulty ground connection. As I said, everything looks okay in the engine compartment. I'll take a look at the wiring harness leading to the control unit tomorrow.

Today it was bitterly cold here, and my garage is full of all sorts of junk.

Best regards,
Marco

Good morning, Marco.

An "auto scan" will not work, but a regular scan will.

The wiring harness appears to be okay. Can you rule out damage caused by a weasel?

The accelerator pedal sensor and the two temperature sensors are directly connected to the engine control unit.

What does the water container look like? Can the water drain out, or have the pins on the engine control unit been corroded due to water ingress?

You should definitely check the grounding connections, especially considering the age of the installation. Ideally, this should be done using a voltage drop measurement.

The voltage at the coolant sensor decreases as the temperature increases. At 20 degrees Celsius, it's approximately 3 volts, and at 80 degrees Celsius, it's below 1 volt.

Greetings.

Michael.

Unfortunately, I no longer have access to the old schematics.

However, when the same fault occurs, a common cause is very likely. I strongly suspect that the mass of sensors, including the LMM (mass airflow sensor) and the 2xTemp sensors, are bundled together in a single cable that runs to the MSG (main system module).

However, the accelerator pedal and brake sensor are not connected to the engine, so a common ground should be located close to or even inside the main control unit (MSG). The sensor grounds are thin and brown. Check the MSG connector and see if the MSG still has a connection from the thick brown ground terminal to all the thin output terminals, or if something might have been submerged and damaged in the water reservoir.

Wir hatten hier schon Fälle, wo die Gebermasse im MSG durch wahr. Da ist wahrscheinlich mal eine ungesicherte +12V auf die Gebermasse gekommen. Ich meine, hier gab es sogar einen Beitrag, wo jemand etwas gebrückt hatte. SI'll look into that later.

Regards,
Guste.

Hi,
You can check the temperature sensors in module MWB 007 for functionality using resistance measurement. The brake pedal switches are located in module MWB 006, and the accelerator pedal position is found in module MWB 002.
Previous speakers have already commented on the simultaneous occurrence of the errors. The wiring from the engine runs together first at the splash guard. I would rule out a broken cable in the area of the tailgate. An auto-check system might monitor this (if present), but I consider a connection with the main control unit (MSG) to be unlikely given the vehicle's age.
hg
Herbert.

Hi there.

Nothing is flooded. The mass connections would also be my top candidates.
I hope the cable colors at the Msg are the same for the ground connection, but unfortunately, I don't have a wiring diagram. Otherwise, I'll have to measure it out.

Does the 35i also have those... um... I'm not sure what to call them... mass terminals on the A-pillar inside the car? The ones where various ground connections are plugged or screwed in?

I'm getting the car this afternoon. It's from a very kind, older acquaintance. He can't bring himself to part with it, even though I already replaced the transmission back in early 2016, and I told him, "That's it, drive it until the end of the year when the inspection is due, then it's scrap."

Was soll ich sagen ... TÜV inspection valid until 11/2022.

I think that the problem shouldn't be the final blow, even though that was the initial assessment when I first chimed in yesterday .

I will report.

and thank you in advance for your tips.

Regards,

Marco.

Quick & dirty test:
Check if any of the temperature sensors are still connected to ground. If not, connect a temporary ground connection and see if all the errors disappear simultaneously.

Also, you also need to get the wiring diagrams and see where the sensors connect. I'm not sure if you can still find them on erwin.volkswagen.de, or if those older documents have been removed. But access for an hour costs €7, so you can quickly and cheaply check if anything is there and, if so, print it out within that time. You just need the wiring diagram for the engine (and possibly the one for the brake lights, if those are more likely to be found in the basic documentation).

Here's the translation:

"Additional information: For a Golf 3, manufactured in 1994, I also had an SLP. The following components are connected to a common ground point from the engine control unit (ECU):"
- Speed sensor.
- LMM
- Elevation booster
- Intake air temperature sensor.
- Clutch master cylinder
- Brake pedal switch.
- Fuel temperature sensor.
- Gas pedal
- Engine temperature

Please check if the values displayed in VCDS for the components that didn't fail are still showing meaningful readings.

According to SLP, all of them are connected together on pins 1, 24, and 46 of the 68-pin motor control unit connector.

I don't know to what extent this applies to the 35i model. However, some degree of similarity can be assumed.

Broken cable in the engine wiring harness?

Area: Body/Engine transition.

Sure.

Thanks again to everyone for your tips.

I had the car there today and yesterday.

I have checked:

Mass connections, battery, motor, chassis - okay.
Fuse box appears to be okay.
Brake light switch 1 and 2 removed and tested.
Throttle pedal sensor connector loose.
Mass connections to the A-pillar are okay.
Message received, opened, viewed, smelled, nothing unusual.


Of course, after disconnecting each connector, I tried to clear the error memory and checked to see if anything changed.

The error cannot be cleared, except that it then switches to a short circuit to ground.

The car still starts, the preheating light is blinking normally, but the car has no power.

Sensors are displaying incorrect values.

One more thing, no matter which connectors I disconnect in the engine compartment, the fuel temperature sensor still shows a short circuit or open circuit to the positive terminal. Shouldn't it show a short circuit to ground when it's not actively being used?

I, for one, have no more ideas; I think that's it for this project.

Hello,

It can't be anything major. There might be a damaged cable to the control unit, the control unit might be flooded, or one of the sensors might be short-circuiting. I would disconnect everything, check the power supply to the sensors, and reconnect them one by one. The extremely low temperatures indicate that the measurement is incorrect.
Tap the wiring harness and explicitly connect the motor control unit housing to ground.

Please search the forum for the pin assignments for the sensors and obtain a wiring diagram.

Best regards, Rainer.

Hello Rainer,

That's exactly how I did it; the error changed from a short circuit to a positive voltage to a short circuit to ground.

Except for the fuel temperature sensor, which stubbornly continued to show a short circuit to positive even after disconnecting the wiring harness from the ESP.

Okay, candidate, let's take a look...

I also thought that maybe the fuse box might have some internal damage.

I need to take a look; I'm going to buy the "So wird's gemacht" book.

I hope the wiring diagram for the 1.9 TDI engine is included. I would then check each cable for continuity, against ground, and against positive voltage.

I searched online for the wiring diagram for the TDI engine, but I couldn't find anything.


Best regards,

Especially to everyone who is also concerned about this issue.

Marco.

Hello,

ich würde mir bei Erwin (siehe Fehlerdatenbank) den garantiert zum Auto passenden Stromlaufplan besorgen. Go online.
For my A3 8L, I once got a book (but I don't remember which one, something about self-repair), which contained wiring diagrams, but unfortunately, they were the wrong ones.
You only realize how important something is when you need it.

Best regards, Rainer.

Hi,
Regarding the wiring diagram, I completely agree with Rainer.
The books by Etzold and Korp are quite good, but especially the wiring diagrams are only representative of the entire model series. The MSG (Motor Steuergerät - Engine Control Unit) has different pin assignments for the same engine, varying from model to model and sometimes even from year to year. I know of three different versions just for the 1Z model.
In your case, without measuring or having a plan, you can only guess.
hg
Herbert.

Hello Rainer and Herbert.

So, firstly, for me, access was only possible with a credit card payment...

But now for the best part... there's no wiring diagram for erwin... great... it works.

Regards,

Marco.