ESP,Display Visit Workshop code P0120 Please help

[alexander patie]

will check the wiring diagram tommorow to see what connections there are in the loom...

and the p0122 and p0123 codes are for the tps.

 

[w124coupe]

marek, i suspect you are looking in the wrong place. it has been suggested (w124coupe?) that this code actually refers to the throttle actuator, NOT the tps. if you have a read here it certainly seems so...

STAR TekInfo

the throttle body itself is possibly faulty, or the loom to it could have been disturbed when you did the work on spark plugs?? i have seen a similar problem with an ml500 before, the cure was to replace the loom, that was nearly three years ago now and still going strong. we did suspect the throttle body too, but on inspection it had already been changed before!

as has been said, some time with an independant specialist should pin it down clearly.

Yes. There is a repair listed for bad connections at the actuator (the plug on the end of the loom to be cut off and replaced).

My own experience of failed throttle bodies has mostly been the pot tracks wearing so the ECU loses feedback tracking where the butterfly is in its arc of travel. Emergency mode is then set....

Not sure if there are differences as this is a USA car? How many pins at the throttle actuator connector?

(as Alexander P has said in a few posts, this is the danger with Generic trouble codes - they cover a number of more specific STAR codes which vary by model and release of ECU code).

I have some stuff going on taking most of my time right now so have been hesitant to post as I can't follow up properly...

 

[MarekW]

(Yes. There is a repair listed for bad connections at the actuator (the plug on the end of the loom to be cut off and replaced). )


Sorry but what is a loom?

(My own experience of failed throttle bodies has mostly been the pot tracks wearing so the ECU loses feedback tracking where the butterfly is in its arc of travel. Emergency mode is then set....)

I took the throttle body apart and it looks like new

(Not sure if there are differences as this is a USA car? How many pins at the throttle actuator connector?)

If I remember correctly there are 6 pins (I think should be same for the whole world)

(as Alexander P has said in a few posts, this is the danger with Generic trouble codes - they cover a number of more specific STAR codes which vary by model and release of ECU code).

Not sure where to start checking the wiring?

Thank you

 

[w124coupe]

Sorry to us Brits, the wiring harness is often called a loom.

The Merc report concerned the 6-pi connector - problems with the contacts in the plug on the wiring harness.

 

[lynall]

To check wiring you will probably have to open the wiring loom up, just carefully cut it open with a knife, then follow each wire in turn and check for damage, give each wire a good tug to see if it has broken internally, you can see if it has as it stretchs, the wires will be either numbered or colour coded.

If all looks okay use a multimeter set to any ohms setting ( i normally use 20k but any will do) one probe in the plug and the other a couple of feet down the wire then wiggle and tug the wire whilst watching the multimeter and see if the wire goes open circuit.

Most wiring faults i come across are normally obvious ie sharp edges, damaged cables hidden under brackets etc.

Just done one this morning bloke has fitted all new discs, pads, abs sensor and exciter rings approx £1000 worth of parts, then brought it to us, 5 mins with laptop and a quick look at the wiring revealed a broken wire, resukt 1K he didnt need to spend, fixed with one heat shrink connector

Hope this helps
Lynall

 

[MarekW]

I testet the wires with ohm meter and it checks ok.

Is it possible that the code must be erased before the new TPS will be recognized?

 

[alexander patie]

the code does not relate to the tps, did you check the link? which wires did you test? make sure you check the 6x throttle actuator wires back to the ecu. i checked btw and there are no breaks or connectors in these wires.

 

[MarekW]

I checked the wires from the plug of trottle actuator down to about 2 feet from it, I did not open the whole loom all the way to ecu

 

[MarekW]

Hi

I finally had the reading from my car with carsoft 7.4 and it has the following info:

Actual error's:

p202e Actual value potentiometer in throttle valve actuator (p0120)

1. Check signal from actual value potentiometer 1
2. Check signal from actual value potentiometer 2
3.Check voltage supply (1+2)

How can I check these values and where and which pins?

Any help greatly appreciated

 

[alexander patie]

just find the same colour code wires that you have at the actuator at the ecu. the black and blue are in one plug and the other four are in another. test all 6x wires for resistance on a low ohms scale. they should be no higher than 0.5 ohms.

i think the black and blue are actator, the other four will be actual value potentiometer 1 + 2. you can EASILY work out what pairs they are in with a meter, then test the resistance in each pair while slowly opening the throttle by hand.

 

[MarekW]

I will do the test tomorrow morning

Thanks

 

[MarekW]

I did more testing

I checked the 6 wires from ECU to the throttle actuator and they are all good.

I checked the resistance on wires going to actuator to one potentiometer and the other potentiometer (two pairs of wires gray and violet and also white and yellow) and was moving the flap of the actuator but there was no difference in resistance, it was a closed circuit.

Does this mean that the trottle actuator is bad or there maybe some other thing damaged?

Thank you

 

[w124coupe]

Hi, sorry to butt in again but there's some confusion here. The actuator works like this:

The ECU supplies power to the motor and "senses" the degree of throttle plate rotation by measuring the voltage from each of 2 potentiometers.

The potentiometers each have 3 terminals: +supply, -supply and output from the "wiper" on the resistance track that rotates with the throttle plate.

So, to test:

1. Blue and black are the supply to the actuator motor. Check there is a resistance there (I don't have the value) to make sure the motor coils are not open-circuit.

2. Grey and violet are the 12v supply to the potentiometers (i.e. to BOTH of them).

3. White is the OUTPUT from one potentiometer.

4. Yellow is the OUTPUT from the second potentiometer.

As with the TPS, the ECU needs the two pots to "agree" on the plate position or it throws a code and enters emergency mode.

Now, to test 3 and 4 you:

EITHER run Star and run the actuator test (this powers and rotates the plate while measuring the two output voltages without running the engine).

OR supply the grey/violet voltage yourself and then measure, in turn, the output at the white and then yellow as you rotate the throttle plate by hand (look for smoothly changing voltage with no "holes" at any point in the travel). Missing voltage or stuttering means the potentiometer track is faulty and a new actuator (or a refurb) is needed.

Does that help?

 

[MarekW]

(OR supply the grey/violet voltage yourself and then measure, in turn, the output at the white and then yellow as you rotate the throttle plate by hand (look for smoothly changing voltage with no "holes" at any point in the travel). Missing voltage or stuttering means the potentiometer track is faulty and a new actuator (or a refurb) is needed.

Does that help?)

Do I supply 5v or 12 to gray and than to violet and measure between gray and white and than supply voltage to violet and measure between violet and yellow when rotating the throttle?

I would like to try this before I go to the shop, and also if the actuator has to be changed does it have to be programmed or reset with the star diadnostics? ( i only have carsoft with multiplexer)

Thank you

 

[w124coupe]

(OR supply the grey/violet voltage yourself and then measure, in turn, the output at the white and then yellow as you rotate the throttle plate by hand (look for smoothly changing voltage with no "holes" at any point in the travel). Missing voltage or stuttering means the potentiometer track is faulty and a new actuator (or a refurb) is needed.

Does that help?)

Do I supply 5v or 12 to gray and than to violet and measure between gray and white and than supply voltage to violet and measure between violet and yellow when rotating the throttle?

I would like to try this before I go to the shop, and also if the actuator has to be changed does it have to be programmed or reset with the star diadnostics? ( i only have carsoft with multiplexer)

Thank you

If it was me, I would:

Supply 5v across violet (+) and grey (-) - these are the "ends" of the TWO potentiometers.

Connect my meter to read the voltage between white and grey while turning the throttle.

Repeat for yellow.

Make sure the measured voltage changes smoothly as you turn with no "drop-outs".

White and yellow both also have a (separate) fixed resistor in series with their pot (the values are not listed) so I can't tell you what voltage you should see.

 

[alexander patie]

thanks for that w124coupe. i had a look on wis today and realised my mistake with the pot wiring! marek is getting some top class advice here.

i personally would have it all plugged in, ignition on, and measure output voltage from the pots. bench testing would be easier, unless you don't have a variable voltage power supply etc.

 

[w124coupe]

thanks for that w124coupe. i had a look on wis today and realised my mistake with the pot wiring! marek is getting some top class advice here.

i personally would have it all plugged in, ignition on, and measure output voltage from the pots. bench testing would be easier, unless you don't have a variable voltage power supply etc.

I have a Maplin battery box with AAs in plus leads with croc clips and needle points - about £5 all up - its proved useful on the W124!

 

[MarekW]

I build an electronic programmer that has a 5v output, I will do some testing this afternoon.

I really appreciate all your help

 

[MarekW]

Hi

I did the Alexander test, and it is as follows:

(My battery is probably low and measurements may be not as accurate)



Measuring voltage when actuator closed and than open by hand :

white and gray = 8.05v closed 11.64v open

gray and yellow = 11.94 all the time no change open or closed

white and yellow = 3.26v closed -3.94v closed

yellow and violet = 11.30v closed 7.86 open

I could probably charge the battery and get some more accurate readings if necessary.

Not sure if it is good or bad?

If I need a new actuator or used, does it need to be programmed or codes cleared before it will work?


Thank you

 

[w124coupe]

Hi, looks like the "yellow" pot is bad.

To double check, please disconnect the plugs and measure these resistances (please let us know the max and min values for each as you rotate the throttle by hand AND check the values change smoothly up and down the range) :

Yellow to grey (this is suspect)
Yellow to violet

White to grey
White to violet