ESP,Display Visit Workshop code P0120 Please help

[MarekW]

I have a 2001 e320 with 103000 miles

ESP lighted up, engine running but unable to accelerate. Display Visit Workshop, the code is P0120.
It starts fine but runs at 1200 rpm and after pressing the accelerator goes to a maximum of 1600 rpm while parked.
When I drive it will go up to 12 miles per hour with the pedal to the floor.

I did some testing

I unplugged the plug from the TPS, than put key in position #II and measured the voltage in the plug coming from ECU to the TPS between pin 1 & 6 = 4.97v
and than between pin 1 & 3 =4.97v.

Later on the bench I supplied 5v (using a power adapter with 5V voltage regulator) to the TPS pin 1+ and pin 3- and measured the voltage between pin 3 & 4 = 0.140v.

Than 5v to pin 1+ and pin 6-and measured voltage between pin 5 and 6= 0.311v

Does this sound like my TPS is working normal and I have some other issues with my car not having response to the gas pedal?

Thank you

 

[BlackC55]

It sounds like a MAF fault.

 

[w124coupe]

I have a 2001 e320 with 103000 miles

ESP lighted up, engine running but unable to accelerate. Display Visit Workshop, the code is P0120.
It starts fine but runs at 1200 rpm and after pressing the accelerator goes to a maximum of 1600 rpm while parked.
When I drive it will go up to 12 miles per hour with the pedal to the floor.

I did some testing

I unplugged the plug from the TPS, than put key in position #II and measured the voltage in the plug coming from ECU to the TPS between pin 1 & 6 = 4.97v
and than between pin 1 & 3 =4.97v.

Good - that means the ECU supply and ground are OK (test value is 4.75-5.25V)

Later on the bench I supplied 5v (using a power adapter with 5V voltage regulator) to the TPS pin 1+ and pin 3- and measured the voltage between pin 3 & 4 = 0.140v.

Should be OK, target is >0.1V for Signal 2 when fed with same as ECU voltage.

Than 5v to pin 1+ and pin 6-and measured voltage between pin 5 and 6= 0.311v

Should be OK, target is >0.2V for Signal 1 when fed with same as ECU voltage.

Does this sound like my TPS is working normal and I have some other issues with my car not having response to the gas pedal?

Thank you

This sensor usually fails at the idle position and is very reliable further up the range.

Merc info says Fault code is set if:

Exsessive voltage difference between signal 1 and signal 2 (at idle position) - The signals may deviate from one another in the idle speed position no more than 8 %. For comparison purposes, signal 2 is multiplied by 2.
(you are slightly outside the deviation spec but are you using an accurate voltmeter and is the ECU really that sensitive?)

Short circuit to positive - If signal 1 is larger than 4.9 V or signal 2 larger than 2.4 V, a short-circuit to positive is present (12 V or 5 V) or the accelerator pedal sensor is faulty.
(you could test S1 and S2 at wide open throttle and see what voltages you get; also test at points between idle and wide open to make sure the voltages are climbing)

Short circuit to ground/open circuit - If signal 1 is smaller than 0.2 V or signal 2 smaller than 0.1 V, the cause is a short
to ground, an interruption or the accelerator pedal sensor is faulty.
(your values are fine here)

Voltage supply - The voltage supply to the accelerator pedal sensor must lie between 4.75 to 5.25V.
(your values are fine here)

 

[w124coupe]

You should also check the wiring to the throttle actuator, the condition of its plug/socket connector and see how dirty the throttle blade is as "the other end" of this.

Has the car been left standing (not driven/run) for a long time?

 

[alexander patie]

tps never suspect. never ever ever heard of a tps failing. have changed 8,000,000 maf sensors though. does not explain your esp light.

what codes were in the esp module??

 

[alexander patie]

i am guessing at voltage supply here, if the fault and code are current.

 

[w124coupe]

i am guessing at voltage supply here, if the fault and code are current.

OP says he has measured the ECU -> TPS supply voltage (S1 and S2) at 4.97V. That wiould indicate the supplies and the ground are OK?

I think I'm right i saying there can be a P0120 set if the throttle actuator connector is playing up (the poor harness connector was the subject of a cut off/solder on/shrink tubing factory repair action).

I wonder if his means of code reading extended to the non-generic codes?

 

[alexander patie]

a glitch on the supply will log the fault which will be taken very seriously by ecu. i would check the wiring to pins 3 and 6 in wis if i could, also pin 1. but it's all at work right now.

star makes this all too easy some times, the tps values as read by the ecu are in the live data and so on and on. working with just a generic reader and no live data, das or wis etc must be hell!

 

[w124coupe]

You should also check the wiring to the throttle actuator, the condition of its plug/socket connector and see how dirty the throttle blade is as "the other end" of this.

Has the car been left standing (not driven/run) for a long time?

I stand by this as needing checking - P0120 generic code covers some MB DTC actuator fault codes.

 

[MarekW]

I have removed the throttle body and cleaned it (it was not very dirty, it looked normal).

I looked at the cable and looks fine no cracks.

The car was driven daily, but running rough lately.
The problem started when I removed wires ( 2 or 3 on driver side )from spark plugs and put them back.

Today I kind of got excited and thought I fixed the problem.

When the car was running I disconnected the air mass flow sensor, than did the tps reset and restarted the car, all power back and I was able to drive with no problems.
After shut down back to the same code p0120, ( I was able to do it 2 times and drive normal)

I have only a generic code reader and it shows p0120 only.

I am not sure what should I try next

Thank you for your input and time

 

[MarekW]

Just wondering if somebody have some other suggestions?

Thank you

 

[lynall]

Brake light switch broken internally , car thinks you are braking so wont give you any throttle?

Switch under £10 from mb dealer got to be worth a try, switch has 2 switchs inside one for brake lights and other for cruise, traction etc.



Lynall

 

[wemorgan]

The car was driven daily, but running rough lately.
The problem started when I removed wires ( 2 or 3 on driver side )from spark plugs and put them back.

Did it sound like it was miss-firing?
Might you have damaged the HT leads when removing them?
What is their general condition like?

 

[alexander patie]

presumably you have erased the code and it returns immediately? if this IS a current fault the star machine will pin it down straight away. obviously you may be faced with testing of loom etc to be 100% sure, but without plugging you in we can not do much. your bench test of the tps shows you have a fair idea of the electronics involved, have you tried checking continuity back to the ecu?? definately worth a try, sometimes looms do fail...

 

[w124coupe]

Can't tell your location so can't be certain which 320 engine/ME type this is - can you please post the start of the VIN 210.xxx and the engine code M112.xxx ? (2000-2001 cuts over the release of the ME system).

Generic code P0120 relates to Merc codes for both the operation of the throttle and of the position sensor.

Are you sure the wiring to the throttle actuator from the ECU is OK?

The VIN etc info will allow us to give you the ECU plug pin numbers to check the wiring to the actuator motor (and its resistance).

(you seem to have tested and proven the TPC end fairly well - still worth going back to check all the supply, signal and ground wires are OK all the way back though)


Have you tried running with JUST the MAF disconnected to eliminate that?


Just keep in your mind the ECU is saying - I can't control the engine via the throttle.....so either the TPS is broken/lying, the throttle actuator is broken/lying or maybe the MAF is producing a voltage within acceptable range but nor related to the air flowing past it and therefore causing the ECU to screw up the mixture.

Disconnected, the MAF will be ignored and a default fuel map used - if it runs OK-ish then the MAF (or possibly its wiring) is at fault.


If this was a 104 engine we would all be screaming "wiring harness"!

 

[MarekW]

Lynall
(Brake light switch broken internally , car thinks you are braking so wont give you any throttle?)

How this switch could be tested

Will
(Did it sound like it was miss-firing?
Might you have damaged the HT leads when removing them?
What is their general condition like?)

I did have misfire on cyl 3, that is why I removed the spark plug wires and put them back on

alexander patie
(presumably you have erased the code and it returns immediately? if this IS a current fault the star machine will pin it down straight away. obviously you may be faced with testing of loom etc to be 100% sure, but without plugging you in we can not do much. your bench test of the tps shows you have a fair idea of the electronics involved, have you tried checking continuity back to the ecu?? definately worth a try, sometimes looms do fail...)

I did not test the continuity yet

w124coupe
(Can't tell your location so can't be certain which 320 engine/ME type this is - can you please post the start of the VIN 210.xxx and the engine code M112.xxx ? (2000-2001 cuts over the release of the ME system).)

I am in Texas the ser # is WDBJF65J71B266xxx, not sure about engine code (I do not have the sticker in the door if it is written there)


(Are you sure the wiring to the throttle actuator from the ECU is OK?)

It looks ok but did not test it

(The VIN etc info will allow us to give you the ECU plug pin numbers to check the wiring to the actuator motor (and its resistance).

(you seem to have tested and proven the TPC end fairly well - still worth going back to check all the supply, signal and ground wires are OK all the way back though)

How can I test all the signals and ground wires, what values should I get and at what pins?


(Have you tried running with JUST the MAF disconnected to eliminate that?)

The car will not run without the MAF.

(Just keep in your mind the ECU is saying - I can't control the engine via the throttle.....so either the TPS is broken/lying, the throttle actuator is broken/lying or maybe the MAF is producing a voltage within acceptable range but nor related to the air flowing past it and therefore causing the ECU to screw up the mixture.)

Somehow I think it may be the TPS, but see my answers and tell me other tests I coul do on my own, otherwise I will need to get it checked out at the dealer or other place.


Thank you

 

[alexander patie]

tps is unlikely, especially with the evidence of your bench test. DOES the fault come back immediately when erased??? if so check the voltage at the harness at the ecu with everything connected. the wiring will have the same coulours as at the tps btw. harnesses do fail.

 

[MarekW]

I am unable to clear the codes, I will check the harness today

 

[MarekW]

(tps is unlikely, especially with the evidence of your bench test. DOES the fault come back immediately when erased??? if so check the voltage at the harness at the ecu with everything connected. the wiring will have the same coulours as at the tps btw. harnesses do fail.)

How can I test the voltage and where should I start?


I installed a new TPS and no change , still same problem

 

[alexander patie]

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.