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VW MKV-A5 Golf/Jettas Discussions area for A5/MkV Jetta/Golf (2005/2006 PD and 2009 CR).

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Old February 23rd, 2019, 10:54   #1
Join Date: Jan 2019
Location: Florida
Default 2005.5 BRM TDI Manual - Intermittent Loss of Power - Accelerator Pedal Suspect

Greetings all,

I have been battling an intermittent loss of power in my 2005.5 manual BRM TDI. The condition manifests itself in the following fashion: randomly (i.e. I cannot get it to assert under any specific set of conditions that I am aware of) when accelerating it feels like the ECU completely cuts fueling to the engine. When it happens, if I step on the pedal to command acceleration, there is no response from the engine (either by seat of the pants feel or by tachometer response). The engine doesn't shut off or anything like that...it just simply begins to engine brake smoothly back toward idle. 1) If I step on the clutch and downshift and reaccelerate the engine responds to the acceleration command normally. 2) OR if I coast long enough (usually 3-4 seconds) and continue to step on the accelerator pedal it usually responds eventually to the acceleration command. 3) OR if I engage the cruise control the engine will begin fueling normally and maintain whatever speed I was at at the time of cruise control engagement.

I have taken my car to the local "guru" who is stumped at what is causing the condition. After much research on this site I have attempted to overtime eliminate the conditions which may cause the ECU to cut fueling to the engine (such as overboost or a bad brake light or brake pedal switch). Like I said earlier, there are no codes associated with the condition and I currently have no engine codes per the VCDS.

I began data logging several parameters I thought pertinent to the problem on my daily drive to work and was finally able to get the condition to assert several times on one drive. I'll post the data pictures to the post (hopefully!).

The measuring blocks that I was recording when it happened include the following:

RPM, Boost Specified, Boost Actual, N75 duty cycle, Injection Quantity Actual, Injection Requirement, Cruise Control Monitoring, and Accelerator Pedal Position.

My analysis of the data recorded during the instances where I lost power is as follows:

- During loss of power there was no overboost condition.
- During loss of power there was no assertion of the brake pedal switch or brake light switch according to the CCM bits (i.e. normal expected indications)
- During loss of power there the accelerator pedal position channel indicated normal readings of my accelerator pedal request (i.e. it didn't drop to zero indicating a loss of the request signal). I could see the pedal position respond to my inputs as I cycled the pedal from zero to 100% to no avail

**What I think is the smoking gun**

1) During loss of power the ECU did not register an Injection Requirement commensurate with the Acceleration Pedal request. It registered 0 injection requirement as if I had let off the accelerator pedal completely (even though the accelerator pedal channel showed I was making an acceleration request)
2) During loss of power when I tried to accelerate using the accelerator pedal while I had the cruise control activated (i.e. I was driving down the road, cruise set, and using the pedal to speed up to pass another car and got no response to the pedal) the accelerator pedal override bit on the CCM channel was never set indicating that according to the CCM recording that I had never pressed the accelerator pedal even though I was pressing the accelerator pedal.

I think, according to the data, that there are times that the ECU stops "seeing" my acceleration pedal request even though part of the ECU "knows" that I am in fact inputing acceleration. Is this an accurate analysis? How could the ECU simultaneously "see" my acceleration request and record it correctly in the Acceleration Pedal measurement block but NOT see the acceleration input on the CCM measurement block?

Is this a pedal problem? A wiring problem between the pedal and the ECU? Or something completely different?

Thanks in advance for all your help and experience.

**Attached are pictures of three instances when the condition asserted. I highlighted in red the exact instance when the ECU would not command fueling to the engine when I depressed the accelerator pedal. I am also including a Cruise Control Switch diagram that describes the bits you should see in the Cruise Control Monitoring measurement block for various conditions.

1) Loss of Power w/Cruise Control Not Engaged

2) Loss of Power w/Cruise Control Engaged #1

3) Loss of Power w/Cruise Control Engaged #2

4) Cruise Control Switch Values

FL_TDI is offline   Reply With Quote
Old March 5th, 2019, 18:44   #2
Join Date: Jan 2019
Location: Florida
Default Thread Resurrection

I was hoping for a more robust response from the crowd, but here is an update to my original post:

I ended up purchasing a used TDI pedal. Same part number and I successfully installed it after much consternation. The first drive on the new pedal was flawless. Everything worked as advertised. Then on my second drive the Loss of Power issue occurred in identical fashion to my original post. It was raining in the morning during my first drive so maybe water somewhere in the system is an issue??? (just a guess but I don't remember it always occurring when it rains).

To restate the symptoms some unknown reason the ECU commands a complete stoppage of fueling to the engine. The ECU registers that there is an accelerator request (in terms of pedal position) but does nothing with it in terms of generating an fuel injection requirement and translating that zero fuel injected into the engine (per those measuring blocks). If I engage the cruise control the engine fuels normally immediately even though the pedal doesn't respond. If I step on the clutch and reengage gears the engine always responds immediately as well. During this entire time there are no detected input signals from the brake pedal or brake light switch registered by the ECU.

To help eliminate the wiring from the pedal to the ECU I then disconnected the pedal from the pin connector and checked the reference voltages to the grounds for both accelerator pedal circuits (Pins 1 to 5 and Pins 2 to 3). The reference voltages showed a solid 4.99 volts on the digital multimeter so leading me to believe the reference voltage and grounds are good for both pedal circuits. Both signal voltage pins showed 0 volts when I checked them with the key on (pins 4 and 6 to ground). It doesn't look to be a pedal problem or a wiring problem between the pedal and the ECU.

Anybody out there with additional suggestions? I'm at my breaking point with this issue.
FL_TDI is offline   Reply With Quote
Old March 15th, 2019, 09:43   #3
Veteran Member
Join Date: Aug 2009
Location: Kansas, USA

My guess is the injector wiring harness. I've replaced that harness on both of my BRM Jettas.

MrBigTruck is offline   Reply With Quote
Old March 18th, 2019, 11:20   #4
Join Date: Feb 2015
Location: Newbrunswick CN
Fuel Economy: 6L/100km

2006 jetta tdi BRM. Possibly I have been having a similar issue. Mine was at one point about two months ago reverting to Idle rpm only. This would last for a few second up to a minute in length. It was throwing Throttle body codes/engine light at the time. The loss of power issue has not returned for about two months now but the engine light is still coming on. I replaced the Throttle body valve/ASV and it did not make the light go away. This may be a related issue but very hard to say. See my post "Throttle Body/ASV giving codes". Sorry I cant offer more..
likediesel is offline   Reply With Quote
Old March 18th, 2019, 11:40   #5
Join Date: Feb 2015
Location: Newbrunswick CN
Fuel Economy: 6L/100km

If you still have access to a scan tool like that try looking at all other sensors and see if one of them is not up to snuff..
Another thing to try is to have an assistant hold rpm at about 2k. You go out and start wiggling wires under the hood. Also gently tap sensors that you can access. See if you co can make your gremlin appear. You can also watch you scan tool during this time to see if anything you do throws a code to your cars computer or if an engine light comes on.

Most Importantly.. Of Coarse you nee to be careful to keep clear of rotating equipment under the hood.. Some people need to be told that gremlins bite.. LOL Good Luck..
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