Throttle Position Sensor TPS 078 133 154 / Bosch 0 280 120 432

[JayCab]

Hello Forum,

I’ve taken the plunge and bought one of these from Audi Tradition to replace my suspiciously failing one…

I can now also settle the official measurement/testing confusion on these with the official 3.6Ko reading from pins 1-3 to judge a “good” TPS. Short: as many suspect, this is incorrect.

…….

The following are the readings from my old and new TPS (both genuine, old is 1999 with 26 years use, new is NOS 2011 unused):

OLD:

installed:
4-6 continuity throttle closed
1-2 1.8Ko all the time
1-3 2.47Ko closed 1.00Ko open
2-3 0.93 Ko closed 2.40Ko open

off car limits:
1-3 2.47Ko closed 0.88Ko open
2-3 0.93Ko closed 2.49Ko open


NEW:

installed:
4-6 continuity throttle closed
1-2 1.93 Ko all the time
1-3 2.62Ko closed 1.03Ko open
2-3 0.96Ko closed 2.57 Ko open

off car limits:
1-3 2.62Ko closed 0.90Ko open
2-3 0.98Ko closed 2.65 Ko open



The difference between installed and off car is because the rotation angle of the throttle plate is slightly lower than the full possible rotation of the sensor. So there is a little bit more turn possible to the end of travel on the TPS when not mounted on the throttle.

The brand new NOS sensor has a max 1-3 pin resistance of 2.62Ko, which is still less than the 3.6Ko printed in the Audi manuals for testing this sensor. It has to be a misprint by Audi, because this is true both at mounted and unmounted travel limits with a new unused genuine TPS.



HARNESS TEST (from a 1999 Cab Final)

Ign On:

1 - 5.14V from Engine Earth
2 - 16.5 Ohms to Engine Earth
3 - 0.558 Mo from Engine Earth
4 - 16.5 Ohms from Engine Earth
5 - NC
6 - 5.13V from Engine Earth

The grounds both have ~16Ohms to the engine earth, which seems high to me. Think I’ll have to go on another ground contact cleaning hunt soon…

……

You may be thinking so far from the tests above that all was well and I’ve wasted my hard earned…

Not so fast..!

The test in the literature is based on reading at the limits. It says nothing about the possibility of dead zones in the low/mid travel range of the TPS.

What I discovered was that at cold outdoor temperature (ie a typical cold start situation) the old sensor gave erratically higher or non contact readings between around 10% and 50% open. This improved but was still dodgy when the sensor was at indoor room temperature or heated up a bit..

I think replacement of the sensor has cured the symptom, which was weird random gear change behaviour in the low throttle range. I’ve only tested for an afternoon / 30 miles sp far, but it seems improved.

Most on this forum will not be driving autos I assume, but on the automatics, the TPS position signal is fed from the ECU to the TCM in a daisy chain fashion so the TCM knows the pedal position, which it uses to make gearchange decisions!!

[JayCab]

[JayCab]

I forgot to add: Thanks be to Colesy

[SteveH]

I bet that was expensive!

[Colesy]

Great work, Jay. Pleased to hear it was a worthwhile replacement.

[Fat Audi 80]

Hi Jay,

Thanks for posting, this is really helpful. I am currently trying to diagnose some boost issues which are showing TPS as a fault code. It appears to pass the rudimentary tests, but this gives me more insight.

Cheers

Steve

[Crasher]

I bet that was expensive!

Not bad at €200 when AutoDoc want £310 for the same Bosch F 026 T03 075. I replaced it on the S2 as there was a hole in it from the accelerator cable rubbing thorough the case.

[SteveH]

Not bad at €200 when AutoDoc want £310 for the same Bosch F 026 T03 075. I replaced it on the S2 as there was a hole in it from the accelerator cable rubbing thorough the case.

Bargain

[JayCab]

Hmm, I’d go with “expensive necessity”. Thankful I could still get it but in electrical component terms a €200 pot is about €199 too expensive.

Second hand ones on eBay go for £50 to £70, and are all as old or even older than the one I’m replacing. I’d rather guarantee a bad value part works at €200 than pay £50 for one that might be broken just the same anyway binning £50 or having an eBay tit for tat which I don’t have time for.

Car part pricing can be annoyingly unfair sometimes, it is what it is. Known territory of running a 90’s Audi.

[Crasher]

For me with used parts it is time, waiting days for it to turn up and then finding it is faulty, that can instantly lose me and a customer any saving. It even applies to pattern parts; with the S2 I replaced EVERY sensor, even the Air Mass Meter. When up and running I had a charge air temp sensor code, that was the new aftermarket manifold temp sensor. Next, I spent hours checking temps and other details, even fitting a better radiator, as the temp gauge was reading too high, that turned out to be the new VEMO temp sensor.