P1128 Error Code and Location of MAF Fuse

[ashfleeburgooben]

Hi there. I am dealing with a constant P1128 error code and after doing a whole bunch of googling today have finally narrowed things down a little.

I replaced my O2 sensor and the MAF about a year or so ago but everything is still pointing in that direction.

Using a Haynes manual I have I decided to test the MAF. One of the steps shows me how to test the electrical connector first by connecting a voltmeter to terminal number 2 and to a ground. I should get 12V. What I actually get is 0.0012V.

The book says if I do not get 12V I should check the circuit from the MAF to the fuse box. I have checked all of the fuses in the box on the side of the dashboard on the driver's side. All are good. I have checked all the fuses in the box on top of the battery. All are good.

So reading these forums I saw mention of a G39 fuse. I have no idea where this is though. Is this even what I'm looking for?

I do have VCDS-Lite as well, though I'm not even sure totally how to use it yet. I just got it a couple days ago and am pretty new to the whole computer end of things.

Thanks for any ideas!

Full Fault Message Text:

17536 - Fuel Trim; Bank 1 (Mult): System too Lean
P1128 - 35-00 - -

[billymade]

Here are some links that might be helpful:

17536/P1128/004392 - Ross-Tech Wiki

Fuel Trim Info - Ross-Tech Wiki


My bentley manual also refers to checking some other things:


SAE VAG Description
P1128 17536 Long Term Fuel Trim mult.,Bank1 System too Lean


Exhaust system, refer to Engine Mechanical - Repair Group 26


Fuel injectors

Fuel injectors, checking

Fuel pressure regulator and residual pressure

Fuel pressure regulator and residual pressure, checking

Fuel Pump (FP)

Fuel Pump (FP), checking

Intake system, refer to Fuel Injection & Ignition - Repair Group 24


Secondary Air Injection (AIR) system, refer to Engine Mechanical - Repair Group 26


Note: check for vacuum leaks

[ashfleeburgooben]

Thanks Billy. Any idea where I can find the G39 fuse?

[billymade]

I'm not familiar with that fuse but take a look at this thread: Fuse Card

[ashfleeburgooben]

Yeah, I found that thread. The fuse I'm looking for is on page 99 of the Fuses & Relays - All Years.pdf that someone posted on there. Only problem is, I have no idea how to read the wiring diagrams to figure out how they relate to the physical location of the thing.

Thanks again for your help billymade. I'm going to start going through your list from your Bentley one by one. I need to get one of those Bentley's instead of this old Haynes manual I think.

[MyOtherRidesAVette]

Originally Posted by ashfleeburgooben

Yeah, I found that thread. The fuse I'm looking for is on page 99 of the Fuses & Relays - All Years.pdf that someone posted on there. Only problem is, I have no idea how to read the wiring diagrams to figure out how they relate to the physical location of the thing.

Thanks again for your help billymade. I'm going to start going through your list from your Bentley one by one. I need to get one of those Bentley's instead of this old Haynes manual I think.

Well, I'm confused. I put up the .pdf. Page 99? Also, no wiring diagram used to locate a fuse on a fuse panel. Just a diagram of the panel. Try to explain what it is your looking for exactly.

Fuse G39? Where did you get that number, what fuse is it your looking for, by function, not number.

And if you are getting a meter reading of 0.0012V instead of 12V it sounds as if you simply have the meter on the wrong setting.

MORAV

[ashfleeburgooben]

Hi MORAV,

Thanks for your reply. I'll try to clarify a little bit about what I'm trying to do here.

I have a Haynes manual right now for my 2000 Beetle 2.0L (if you know of a place to buy a digital downloadable copy of the Bentley I am all ears!).

In it there is a section for the Mass airflow sensor check and replacement. It recommends that before testing the MAF operation to check the voltage supply circuit. These are the steps it suggests.

1. Disconnect electrical connector and connect positive lead of voltmeter to terminal number 2 and negative lead to a ground.

2. Turn on ignition and voltage should read approx 12V

3. If not approx 12V check circuit from MAF to fuse box (check fuses first).

So that's where I am. I am trying to figure out which fuse is for the MAF. To be honest, I'm not sure where I found the G39 fuse information anymore. It may even be the incorrect information, but either way I have been unable to definitively tell which fuse controls the MAF circuit.

I have double checked and verified that all fuses in my fuse box on the driver's side of the cab are good as are all of the fuses on top of the battery in the engine compartment.

I put the voltmeter on again today and verified that it was working by testing the battery and the ground I have been using. I got 12V that way, but when I tried the MAF connector I got 0.005V (key was turned on to ensure power was running.

I have attached an image. Maybe you can see if I'm doing something wrong? And also it's hard to see in the photo but the meter is set to DC Voltage.

[MyOtherRidesAVette]

I'm going to shut down and reboot my computer, but in the meantime, go to www.bentleypublishers.com You want the New Beetle "Repair Manual" DVD-ROM and I'm sure it is available for download as opposed to waiting on a disc. Be aware though, that it is not written for the novice, that's the paper "Service Manual". Not that an individual can't use it, but it's written more for a learned tech than a DIYer. Wiring diagrams are in both (the paper is simply a print from the DVD, but the paper are about useless, very small hard to read print, and the DVD-ROM links many things within the diagram to other diagrams with the click of the mouse. In the paper, they are not even crossed referenced. You have to go hunting. And they are NOT done like American auto wiring diagrams, so it's almost like a language barrier, till you undersatnd how to read them.

I'm going to load up my Repair Manual and see what I can find for you. I'll post up a capture for the MAF wiring diagram, so you can see what I am talking about.

Be back in a few.

M.

[MyOtherRidesAVette]

Heres the section of the wiring diagram that contains the MAF sensor.

Following the diagram, I find the power is supplied through Fuse Position #43 [10A (red)] (see bottom of post) the input lead is the blue/yellow (position 2 in the connector), I believe, this would be where you would read 12V, and you should be.

Maybe check the wire, just upstream of the plug connector if your not getting a reading in the plug. 0.005V are NO Volts.

Doesn't look bad, let me know if you need it larger, I can capture it differently.

MORAV

[ashfleeburgooben]

MORAV, Thanks so much! I think we are finally getting somewhere. I did a physical check of the fuses initially and all appeared good, but now I went through this the meter and checked each and every single one. Turns out there are a few fuses which show no voltage! They are:

43 - Engine Control
28 - Fuel Pump
32 - Engine Control - Injectors
34 - Engine Control

EDIT: Should mention that I replaced the trouble fuses with known good (receiving power when in other fuse slots) fuses with the same issue.

There seems to be a common thread here. To be honest, should the car even be running? It really does seem to be describing the issues I am having though, fuel too lean code, takes a couple attempts to start every morning (fuel and injectors warming up?), not great mileage.

The only problem now is, where do I go from here? I don't even know where to start.

[MyOtherRidesAVette]

When you say no voltage, I assume the fuses are good but there is no power source? Is this correct?

Have you looked at the Fuse Box on top of the battery? Without looking to see where this power is supplied from, I think you need to have a look. Gonna' take the dog out and then look at more wiring diagrams.

M.

[MyOtherRidesAVette]

Okay, your issue is solved (well mostly). I couldn't wait for your response(s) because my Grand Daughter is having a big Birthday (5th) shindig tomorrow at an exotic animal ranch and I don't know how much time I may have so I went ahead, diagnosed the problem, and prepared the documentation to back it up.

So all might learn here, I want to walk everyone thru a few basics.

You thought the fuses were bad. I don't think so. Your MAF sensor is probably fine also. And me thinks you can throw away billymade's list, even though that is what the code is indicating. Here's the Ross-Tech Wiki take on your P1128 DTC. Go here to source DTCs (the bible for this - better than the Bentley) -
Category:Fault Codes - Ross-Tech Wiki

17536/P1128/004392 - Fuel Trim; Bank 1 (Mult): System too Lean

Possible Symptoms

• Malfunction Indicator Light (MIL) active

Possible Causes

• Mass Air Flow (MAF) Sensor faulty
• Oxygen Sensor Control faulty
  • Oxygen Sensor(s) faulty
• Fuel Injector(s) faulty

Possible Solutions

• Check Mass Air Flow (MAF) Sensor
• Check Oxygen Sensor Control
  • Check Oxygen Sensor(s)
• Check Fuel Injector(s)

Special Notes

• Additional Information on Fuel Trim

Retrieved from "17536/P1128/004392 - Ross-Tech Wiki"

In your case ALL item have failed, or are intermitently failing as you drive

I think if you will use your multimeter, volt meter, and check the fuse receptacles with the subject fuses pulled out you will find both sides are dead. Actually you only need to check the upstream side, but I don't know which side that is without seeing the back of the panel, and why pull it out (typically though it is the left side).

Fuses themselves, can be checked most easily, if they are not visible blown, by doing a continuity test, from prong to prong.

I have put up a .pdf explaining how to read the Bentley wiring diagrams, and I have put up a .pdf file of the entire circuitry for all four fuses in question. Easiest to follow if you will open and print these two files.

Now, to your problem. All four fuses are downstream of the fuel pump relay which is temporarily powered up when you open the door to prime the fuel pump. It is again powered up when you turn the ignition key. The four fuses in question are powered by the lead coming from fuse battery fuse box, fuse S163, and these are the only fuses on this circuit. This circuit is indicated by the yellow highlighted flow line, running from page to page of the wiring diagram, on the last page it connects to the fuel pump relay and the services the four fuses in question downstream of the relay. There is a whole list of components that these fuses power, including the fuel pump itself. With an interupted power stream to these item it is no wonder you Bug is running like $hit. The orange highlighted flow chart shows the lead that powers the ECM which inturn activates the fuel pump relay. I think if the ECM were having power issues from this feed you would be having other issues. First thing you need to check, as I recommended in my earlier post, is the battery fuse box. If the fuse box shows no apparent damage, burnt connections or wires, blown fuse, or meltdown, your problem is either the ECM gone bad or the fuel pump relay gone bad.

The fuel pump relay is in Pos 4 on the main relay panel. It is marked "409". Be sure your on the main panel and not the auxillary panel. I would replace this relay first. I think this will cure your problem. If not then you will need to lok to the ECM.

I hope you bought that paper Bentley I sent you the link for, and btw, if you want A DVD-ROM, I have a new, unopened one, never registered for sale, for $80 shipped.

MORAV

[ashfleeburgooben]

MORAV you are awesome. I have really learned a lot going through this issue. I pulled and replaced the Fuel Pump Relay after checking the battery fuse box (fuse S163) and now get power through all the fuses that were not powering up previously.

One quick note, they only get power when the car is actually running. They still show as dead with the key out of the ignition or in and turned on. A little weird, but okay, it's getting power now.

So hooking up the VCDS and following the instructions here...

Fuel Trim Info - Ross-Tech Wiki

Looking in Group 32 I should have readings within 10%. My first reading (idle) is about 3% so all good. My second reading though hit as high as 25%. So incoming with the new MAF which is where this all started.

It's ordered and will be here in a couple days. I'll keep this post updated.

Thanks again! Also, I did buy the Bentley you recommended. I might also buy the DVD that you are selling, but after all these parts and things I might have to wait just a little while.

[MyOtherRidesAVette]

Damn buddy, I'm glad I could get you up and running. It was funny, it takes a little time to peruse all the pages when your doing it on the computer and having to enlarge them to read, move, enlarge, etc. Once I followed all the fuses back to their power source, and found it to be the fuel pump relay, it was likle a light went off, exactly what I was searching for. The common denominator.

Yes, I can believe that is possible, I'd have to look a little closer at the schematics at some other things, but I don't believe there is anything in those circuits that needs to power on until the engine is cranking, and I think that is probably what you mean (and what is actually happening) when you say "when the car is running"

If you'll look there is a door switch in a different part of the circutiry on the diagram that sends a signal to the ECM when the driver's door is opened, and this in turn (somehow, and what I have to still learn) pre-primes the system. You should here the pump prime for a second when you open the door after it has set for a long length of time, which I assume is triggered by something related to sensing the fuel pressure, or a pre-programmed time frame. Check that out first time it sets over night or all day. I, however, do not here it in my '05, 2.0L

Btw, glad you snagged that paper Bentley, my extra DVD-ROM will probably be around, I haven't been pushing to sell it. Just mention it occasionally when someone "thinks" they can live without it! I buy both whenever "to good of a deal to pass up" crosses my computer screen.

Post up when you get the MAF swapped out. Let me know if you need anything. (p/m me, I don't always see thread postings).

Going to start working on another thread with a similar, but different issue, dead Fuse #29, also engine related.

Oh, and thank you for tolerating my walking everyone through it and posting up the related information. No one learns anything from someone simply throwing out the answer without throwing out the why.

M.

[Beetle Novice]

I just wanted to say thanks guys for this thread! Had the very same issue with not being able to reset the damn code after replacing the MAF sensor. I replaced the relay and cleared the code and SUCCESS!

I just wish I was able to know if the MAF was bad before I replaced the relay, it would have saved $100!

Car runs better, light is off....the world is a nice place once again.

Mike

[MyOtherRidesAVette]

[ashfleeburgooben]

Just thought I'd follow up on this thread as the situation is still not entirely resolved on this end.

With the relay replaced it didn't take long before the same old CEL light came on. I finally gave up and took it to the dealer. They diagnosed the PCV hose as the issue and ordered me up a new one.

It came in today and I'm more than capable of changing a simple hose. Opened the hood, took off the brackets, jiggled them a little to see how tight they were and CRACK. The crankcase breather cracked at the bottom slightly. It's still in place and not wiggling or anything but it is definitely cracked. No one in the city has one in stock so I'm waiting for a replacement to be shipped.

So the question is, safe to drive? If not it looks like I might be out a car until next week! Oh noes!

What do folks think?