# B5.5 passat, 2.8L 30V VERY sluggish acceleration commanded by computer.....



## firehawk6188 (Jun 16, 2011)

Ok, when taking off, I watch the throttle pedal position on vagcom. It's reading properly.

I watch the throttle plate opening, it reads properly, here's the deal:

I can press the pedal 50% when taking off, the pedal reads 50% on vagcom, but the computer only commands say 10% on the throttle body resulting in acceleration that is terrible.

It does this more often than not. Once in a while I press 50% and the throttle actually opens 50% and the car takes off fine then.

WTF gives? 

NO codes, TB is clean, vacuum hoses are all good, I have done throttle alignment in Vagcom. Why in the world would the computer only command such a small throttle plate percentage?

If I floor it then the computer commands 100% and the car goes fine......

I am really fed up with this.....


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## Slimjimmn (Apr 8, 2006)

watch the tps voltage with car off key on and slowl depress the throttle pedal and watch for a voltage spike up/down. You might have a bad tps in the throttle body or a shorting armature.


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## firehawk6188 (Jun 16, 2011)

Slimjimmn said:


> watch the tps voltage with car off key on and slowl depress the throttle pedal and watch for a voltage spike up/down. You might have a bad tps in the throttle body or a shorting armature.



Good advice. I did check TPS readings, throttlebody readings, ECU commanded percentages etc etc etc all are perfect.

I found the problem. Defective brake light switch.


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## Slimjimmn (Apr 8, 2006)

how did that possibly correlate to sluggish accell? did the switch break and push the pedal down?


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## firehawk6188 (Jun 16, 2011)

Slimjimmn said:


> how did that possibly correlate to sluggish accell? did the switch break and push the pedal down?



No.

Go try it if you have a B5 passat. Hold your foot lightly on the brake and just give it a little gas.


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## firehawk6188 (Jun 16, 2011)

I know for fact this fixed it.

When the computer sees brake pedal applied it definitely changes the throttle map. The amount of throttle body opening vs pedal position is drastically different when the ECU sees brake pedal on vs. off.

The brake light switch in my B5.5 passat is 2 seperate circuits. One is strictly for the brake lights, the 2nd is tied into the computer.


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## Slimjimmn (Apr 8, 2006)

ok I understand. Its programmed into the ecm that when it sees the brake and gas applied at the same time it activates the traction control and reduces throttle output. VW has put that in their cars since 2000 I believe. Its a fail safe mode. Something toyota engineers never put in their cars with drive by wire.


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## Gmanns (Jan 26, 2014)

*Sluggish acceleration caused by brake light switch*

I have been wrestling with this problem and stumbled across this post.
Question, is your vehicle a 4 Motion?
Reason I ask is it seems the brake signal activates traction control.
Since mine is a 4 motion, would this situation necessarily apply?
Gmanns


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