E39 went into limp mode and scanned for codes, found p0120 and p0100. Deleted codes and p0120 code stays, p0100 goes away but will come up when trying to start car. This all started on a hot Arizona night, about 100-105 degrees out (112 degrees earlier that day). I had gotten a code previously for a camshaft position sensor for the passenger side, I do not remember the code. I went ahead and replaced the sensor, car was driving normal but would hesitate at higher rpm’s.. Later in the evening I was accelerating heavily to merge on the freeway, boom. My car goes to limp mode and I figure maybe the throttle body connector got loose or something. I went ahead and replaced it with a working used one.. Car still goes into engine failsafe mode.. I go ahead and replace the throttle pedal now, still nothing. I replace the connector to the throttle body, and still the darn p0120 code. I pulled the ecu out and found no corrosion. Im completely stumped. Any ideas or advice would be greatly appreciated. Thank you
You replaced the TB connector or the TB?
What year 540?
When you replace the TB the DME needs to learn the different positions of the TB.
Did you turn the key to position 2 and leave it there for 30+ Seconds, then turn the key off?
You then start the engine.
I had mine replaced (on E53 X5 4.6is, same part #) with OEM VDO and had similar symptoms. Returned it and got new BMW Genuine TB and no more issues.
Not saying that is your problem but it could be.
I've read later I wasn't the only one having problems with VDO TB.
P.S.
I just realized you replaced it with used part so my theory probably doesn't apply.
Last edited by BMW540san; 07-11-2022 at 09:21 AM.
2010 BMW M6 SMG Coupe * Black Saphire Metallic * Full Leather Merino Black
2019 BMW X3 M40i * Alpine White * Mocha Leather
Former:
1997 BMW 532M (528i with 3.2 S52 engine from E36 M3 / 5 speed manual)
1998 BMW 540i 6 Speed
2003 BMW M5
Yes.
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I’ve had throttle body problems in the past so over time I accumulated 5 oem used throttle body’s, all working. They all have park on my buddies 540i, I stopped having engine failsafe message after retrofitting the facelift throttle pedal
If I may barge in here, I believe the problem is often the connector and connections (wires) of the TB to the DME, And not the TB itself.
How may miles on the engine?
I haven’t looked up those codes yet. I’m wondering if your CAT’s are starting to get clogged.
Last edited by JimLev; 07-11-2022 at 11:54 PM.
I checked continuity from TB to connections at dme, also pulled back the loom to see any chafing. Everything is intact and no abnormal wear. I even moved the loom and wires to see if thereÂ’s a momentary disconnection due to engine movements.. Everything seems normal to me. Small, but probably big detail I left out. I found the secondary o2 sensor harness on passenger side to be shorting out (on ecu side).. Possibly might have an electrical short in the dme now..
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Engine has 90k miles, chassis has 235k. I don’t have cats on my car.. :/
Roman, thanks for the answers.
So now you only have P0100 now, correct?
The power for the heaters in the O2 sensors comes from one (or 2) of the fuses in the back of the DME box, can you check them.
The MAF get power from F1 in the DME box.
The car drives OK until you start flooring it and getting the RPM’s up past 4K or so, right?
Is the DME the same one that came with the car? If so it will have the same VIN number on it.
MAF Wiring.jpg
MAFPg1.jpg
MAFPg2.jpg
Last edited by JimLev; 07-12-2022 at 08:12 PM.
My car has p0120 code at all times right now, regardless of deleting codes. My car does not run for more than 2 seconds, i have no throttle input from pedal. Once trying to start the car I will get a p0100 on top of the p0120
If you’re talking about the little fuse box inside the dme that holds I think 6 fuses. I’ve checked them and there are no blown fuses :/
As far as I know the dme is the original.. The owner that I bought it from previously (4yrs ago, was kind of sketchy)…
P.S. I went ahead and applied heat shrink and electrical tape over each exposed wire coming off the o2 sensor.. It’s tucked up away under the rear heat shield, so no more exposed wires now.
Thanks for reply Jim
Last edited by Romanleal99; 07-12-2022 at 09:52 PM.
To whom it may concern, I’m having a very similar case as this thread -
https://www.bimmerforums.com/forum/s...ngine-failsafe
When the OP and Randy get to measuring the MAF sensor, I have the same values
Pin 4 to pin 5 0v
Pin 4 to ground 5v
Pin 5 to ground 5v
According to Randy the sensor return plane is showing 5V, meaning it's not connected to ground. The values should be
Pin 4 to pin 5 - 5v
Pin 4 to ground 5v
Pin 5 to ground 0v
Randy and the OP then measure voltage from different pins located on the ecu, which I have done, but didn’t right down my values.. They end up taking the conversation offline leaving the thread as a dead end. There was a reply 5 years later from the OP saying they reground the sensor return plane. Not sure what that means, and I’m not sure what sensor(s) they repaired.
Randy makes an appearance in a different thread here - https://www.bimmerforums.com/forum/s...round-Question
He gives a brief explanation of the procedure they went through, and they successfully started the car by bridging a connection… Like before what connection and how did they bridge it? Im unsure.. I have a full wiring diagram of the ecu I pulled from alldata at work… I know I’m doing something wrong but I did test ground from ecu to chassis ground and found them to be grounded..
Like most, electrical is not my strong point, but I tried everything in my power to narrow the situation down.
Thanks
Last edited by Romanleal99; 07-12-2022 at 11:05 PM.
OK, so P0120 says it’s the throttle/pedal position sensor A circuit.
Have you ohmed the wires from both the pedal pot and the TB back to the DME connector?
My intermittent Engine Failsafe Program when on for years until it started doing it a few time a day. I replaced the TB and pedal pot, didn’t help at all.
I checked the connection (ohms) from the connectors back to the DME, they read good, but it was still crapping out.
Finally I replaced the TB connector, the MAF connector, and their pins. Also new wires from the pin back 1/2 way to the DME.
That was 5 years ago, knock on wood, no more Eng Fail Prog since then.
The P0100 is the MAF. Try unplugging the MAF and see if the engine will run for more than 2 seconds.
I have no been able to measure the ohm readings from either TB or POT.
I replaced the TB connector and pins about halfway like you did yesterday. I also have a used low mileage maf connector harness I pulled from a totaled 540i with 60k miles. I didn’t wire that in yet but I’ll give it a shot tomorrow.
Disconnecting the maf had no effect on how long the engine stayed running..
Replaced MAF sensor harness today, no change… wired it all the way into the black box that sits above the injectors and coil packs
Time to start taking some voltage and resistance measurements.
Post up some info and I’ll check my readings.
Do you know exactly what i should be checking? Also this is the wiring diagram im working with. Im not sure if the pages will be sent in order but the page number is at the bottom right corner for reference. I wasnt able to upload a panoramic photo, but each wire is numbered when going from different page
page 1.jpg
page 2.jpg
page 3.jpg
page 4.jpg
Last edited by Romanleal99; 07-13-2022 at 11:07 PM.
I’m working on it, more tomorrow.
Nice prints, easier to follow than what’s in the Bentley manual.
What voltages are you getting at #1, 2, and 3 with the key in position 2 and while cranking?
52F3EF1A-8B2F-48FC-A164-0C4171FB0D48.jpg
233BFE84-E47F-4D75-B7E8-6822CB59765A.jpg
78C7CE88-D159-42FE-802E-19256CC1C1C6.jpg
Yeah real oem has this program that makes following the wires a dream. The dealership I work for provides access for me to use it.. Anyways
Position 2
#1 11.40-11.42
#2 11.42
#3 11.38
While cranking (fuel pump fuse pulled)
#1 8.15-9.20
#2 9.22-9.39
#3 8.14-9.26
I should add that i measured pin location 2,3,1 in that specific order while cranking so voltage does differ after cranking engine for apox 5 seconds on each test. Position 2 was done in order from 1,2,3.
Battery voltage from car right now is 11.5v
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