E36 M52 IAT sensor and Coolant temp sensor.

[Trun1990]

Hi

I am trying to diagnose a problem where my car is running extremely lean on idle.

I have narrowed it down to the IAC. I have a error on the code reader saying short to ground -37 degrees ish.

I am trying to find the point were the short is or the break in the wire is. But not being very successful.

Does anyone have any experience or know a common area where they break. Or i was wondering if it has anything to do with the coolant temperature sensor wiring as i see that splices into the ground wire. Would a break in the CT sensor ground effect the ground of the IAT?

Does anyone know where in the lool the splice is?

I have changed the IAT Sensor for a new one which i have tested and worked correctly.

Any ideas would be great

Cheers

[MarcoZandrini]

Hmmm, I don’t think you have a short to ground but an open circuit. Why? That temperature sensor is a thermistor. A thermistor is a resistor that changes its resistance as its temperature changes. Almost all thermistors are negative coefficient thermistors. That is, as its temperature increases its resistance decreases. So, if the scan shows a very cold temperature as yours is, then the circuit is open. If the circuit was shorted the scan would show a very high temperature. An example is the ambient air temperature sensor in an E46. It’s located in the space between the left front fender liner and the front bumper. Many owners have had this sensor torn out by road debris. The result is the onboard readout shows -40*C unless the wires are shorted together. Then the readout shows 122*C. These 2 temperatures are the lower and upper limits of the read out circuitry, respectively.

[dworthy]

Marc,

Remember the E-36 is slightly different than the E-46 as for the location on the Exterior temp sensor, for the E-36 puts it in the brake duct work.

The IAT is actually located in the intake, just to the right of the throttle body, on the underside.

Next would be to test the sensor, and if it turns out good, check the wiring from the DME to the sensor.

[Trun1990]

The result is the onboard readout shows -40*C unless the wires are shorted together. Then the readout shows 122*C. These 2 temperatures are the lower and upper limits of the read out circuitry, respectively.

Its funny you say that becuase the code comes up as short to ground -37 degrees but when doing live log on INPA is shown 120+ degrees. But i jist thought it was an anomily and didnt think much of it.

@Dworthy - i have check the new sensor that i replaced the old one with and it all seems to work fine.

So it is a break in the wire or a short in the wire. Either way im guessing it is physically looking at the wires and looking for damage? Is there a way of finding the area or pin pointing where the damage is? As its a bit of a pain rputing the wires all the way back to the DME.

[dworthy]

Yes, check for physical damage, and you can pull the DME connector and probe from there with a multi-meter.

[Trun1990]

Yeh ive found out that its pins 14 and 39 on the DME connector. I am pretty sure 14 is live and 39 in the ground?

What test should i do from the DME connector side and what kind of values should i be looking for?

[dworthy]

You should be looking for the same exact or very near, values you would get at the sensor. We call it back probing, or doing a pin-out test.

[Trun1990]

Cheers Dworthy are you or anybody able to tell me the proper way to test the wires from the DME connector as i have been researching alot recently on how to do it. Think i have been testing it correctly but want to make sure.

Would testing the continuity from pin 39 to the plug on the sensor side tel me if theres a break or short in any way.

[dworthy]

Do you have a copy of the ETM? That is BMW's wiring diagram for the E-36.

[Trun1990]

Yes i do Screenshot_20190612-115953_Chrome.jpg
This is what ive found.

[ross1]

A faulty temp sensor that is indicating very cold temps won't cause lean running, it would cause the opposite.
Lean running at idle? I'd be looking for vacuum leaks

[Trun1990]

I have look for leak loads of time using all the different ways and cant find one.

I have had the temp sensor showing very high temperatures aswell. This will make it run lean!

Maybe the short error come up when i was testing with the multimeter?

I had these results from inpa with ingnition on. Cant seem to get the live analysis to work when i turn the engine on, INPA just crashes.

20190531_155942.jpg

[dworthy]

What faults do you get from INPA when it crashes?

Do you have the firewall turned off?

What type of cable are you using to connect?

[Trun1990]

This is the problem im having really getting mixed messafes. I need a definative way to test the wire and connector so i can find the problem.

- - - Updated - - -

Im not sure about firewall but pretty sure i dont as the laptop aas an old one which i completely wiped and i havent installed one since.

I have the blue obd2 cable with the correct chip in ( cant remeber the name) and the normal round connecter which ive soldered the pins on so i can flash tunes onto the DME
Which i know works as i have been able to read and flash tunes to the DME.

I will try and find the error

[dworthy]

Are you connecting using a USB port, or the serial port in the back?

I am going to assume you are using windows XP on that old Dell D830, as I have one as well.

[Trun1990]

Yep into the usb and yep windows xp

[dworthy]

Okay, let me know what error you are receiving.

[Trun1990]

Will do

Do you have any more info on how to test the IAT wiring from the DME connector?

[dworthy]

What I would do is test it like you are testing the sensor without the wiring connected, as there is only 2 wires, find the two that go back to the DME. If one is a ground, then test the one wire going back to the DME and a good ground.

[Trun1990]

Okay so im back home and testing the wiring now.

Im abit confused as on the diagram i put before it says that the ground wire should be grey and brown, and the power/signal wire should be grey.
On my car i have a brown wire and a red and white cable.
So assuming the brown=ground and red/white=power...
The test im doing is -
- from battery positive to ground (brown) terminal on sensor plug = 5.32Volts
- from chassis ground to red/white (power/signal) wire = 11.8Volts.

This all done with the ignition on and the IAT sensor unplugged.

Are these readings rights? I thought it should be the other way round.

[MarcoZandrini]

I think you’re overthinking the problem. First you need to check wiring from the DME to the sensor’s connector. That should show 0 ohms on both wires. Then plug the sensor in and recheck the resistance. I don’t know the resistance you should see but it should be infinite (open) and it should be 0 (short). Then you need to check the DME itself. I’d unplug the sensor and see what the voltage is on both sides of the sensor’s connector.

Darin, what voltage does the DME send to the sensor? 5VDC?

[Trun1990]

Im just trying to understand it all to be honest. Im a nut and bolt man....this electronics goes straight over my head.
When you say replug the sensor. Do you mean plug it in and back prob it into the back of the connector when its plug in. ThenThen connect other probe to the dme plug? Also do you mean it should show any number of ohms, if it shows 0 ohms its shorted?

Sorry mate need to break it down so i understand, as i say im not too savvy on the electronics

Appriciate the help though!

[dworthy]

Correct, you want to test the wire, and the two ways to do it is by plugging it back in and back probing from the DME. If you see something different at the DME pins vrs from when you tested the sensor, it will be time to find the bad wire or connection. This is the second way of checking wire, while not 100% it can tell you if one is broken or not, like Marc said above.

The more advanced way will be to do a voltage drop test, you can watch youtube for those.

[Trun1990]

Update...

I found a break in the wire. All fixed and now the sensor is work correctly

The car is still runnin stupidly lean on idle though. Anybither ideas what it could be?

[dominator293]

Could be a faulty O2 sensor, might be a good place to start.