Resistance at harness to ECU or ICM

[betsy325e]

I read somewhere that all wires connecting (with the component disconnected, obviously) to ECU/ICM should have zero resistance. Can anyone confirm this?

[AndrewBird]

Yes. Wire will have no measurable resistance.

[betsy325e]

Do you know if any resistances change coming out of the ECU to into ICM?

For example, if I measure a temperature sensor at the sensor I get X ohms. If I check it at the ECU I still have X ohms. Checking it at the ICM I've got significantly less than X ohms.

[betsy325e]

Update:

My follow up question contained inaccurate information.

Tested wiring as follows.

Coolant temp switch ground wire to G103: Solid ground. No problemo.
Checked all grounds for ECU and ICM: No problemo.
Checked continuity from ECU pin 13 (coolant temp sensor) to ICM pin 11 (coolant temp sensor): no problemo.

Checked continuity from positive end of connector to both ECU pin 13 and ICM pin 11: Problemo? I'm picking up about 400 Ohms, while I think the wire's resistance should be none. Is that right? It should have zero resistance in the wiring, and the 400-500 Ohms is going to throw off whatever the ECU/ICM does with that resistance measured at the coolant temp switch, right?

I assume that end of the harness goes to a connector/junction of some sort before heading down to the ECU. 1987 325e (manu: 9/86). Does anyone know where that connector is and what pin the temp. sensor is? I'd like to try to track down a fault in the wiring.

[RobDog]

Have you checked the main engine harness connection, the C101? This is the big round connection next to the fuse box and above the brake booster.

[betsy325e]

I have not. That was another question I had: Isn't C101 just engine harness connection to dash cluster, or does it also run to ECU?

On some forums I've seen that it connects to ECU, but pinouts I've seen suggest it just provides signals to dash.

[RobDog]

The c101 goes to both the cluster and the ECU. If you look you can see where 3/4 of the wires run to the passenger side through the firewall and into the glovebox to the ECU.

[betsy325e]

Took a peek in there. Looked brand new. My 500 extra ohms was from a resistor in the wiring that is not marked on any of the diagrams.

[TobyB]

I've never run across a resistor in the wiring. Where was it?
t

[betsy325e]

It was literally in the black insulation near the connector on the wiring. I should have taken a picture of it before I patched it up.

I am sort of curious if it's supposed to be there, but the car idled just fine with it there before.

If anyone is curious without wanting to cut up the rubber boot on their coolant temp. sensor, just measure the resistance between the contacts on the sensor, and then measure the resistance at your ECU or ICM. If you've got this resistor you'll be adding 500 Ohms to whatever reading you got at the sensor.

[betsy325e]

Is everyone's connection to their coolant temp. sensor blue/white? I've got a light brown one, but the wiring coloring inside the connector is the same as marked on diagrams...

I know it's not the one pin connection to temp. gauge. and I've still got a brown for the thermo time switch.

[TobyB]

That resistor sounds like a backyard 'fix' to me...

...and blue/white sounds right. The colors did seem to vary slightly
over the years, and I did find that a couple had changed before or after
the ETK said they were supposed to. As in, sometimes 'after 8/87' actually
applied to a 2/87 car... or 'until 12/94' was not present in an 11/94 car, and so forth...


t

[betsy325e]

I've seen the blue connectors on most of the later models/and i's.

I was sort of guessing maybe the resistor is in there for the ICM in etas and was ditched once they got rid of the ICM for whatever reason.

Doesn't look like anyone soldered it in there -- def. looks like it's from the factory and was nicely encased in the rubber boot (which obviously hadn't been mucked with) just before the connection.

1. Does anyone know anything about this resistor? Anyone with an E? Could anyone with an E do a quick resistance measure at the sensor itself and then at the ground pin 4 and pin 11 on the ICM harness? I'm legit curious if I'm the only person adding 400-500 ohms from the coolant temp. sensor at their ICM.

2. Does anyone know if there is a resistor in the temp-time switch? The brown plug on that looks similar to the connector on my temp sensor.

[betsy325e]

BROWN coolant temp. sensor (not for dash)

Update.

Was going through my box of spares/junkyard pulls. I happened to find the coolant temperature sensor that was originally on my car when I bought it ages ago. I assume it's the original. And it's brownish/yellow ugly like this guy: http://www.ebay.com/itm/TEMPERATURE-...-/200970612283 -- not the expected white or blue. The connector for it on my harness is brown (and it has what I assume to be is a resistor in there at the rubber connector...not sure exactly what it is, but it definitely produces 500 ohms resistance -- checked on the wire on both ends of whatever it is).


That extra 500 ohms coming back to my ICM (which, I think ought to be telling my engine to warm the eff up by constantly givin' it a little more gas) is driving me nuts given my high idle...would really like to know that it's designed that way so I can rule it out.

Anyone know what's up with that?
Is there anyone nerdy enough to help me out?

Thanks

[betsy325e]

Much googling revealed this:

"In the 1980 BMW did a campaign on some of the M30 engined cars.

install an external resistor in the wire for the temperature sensor that feeds the Motronics (should be the one with the light grey connector) Resistor type is 270 ohm, 1/2 watt, "Gold Band" metal film resistor for Motronics Control Units with a Bosch code date of 342 or higher (production date after 9/83) and for Motronics 341 and lower (9/81-9/83 production dates), it is a 560 ohm, 1/2 watt "Gold Band" metal film resistor .


This upgrade was performed at no charge, but may not have been done on your vehicle. If you have the slip on rotor instead of the bolt on type, the full upgrade was not done, but you may still have the external resistor installed under TSB 11 11 84 (920), which was only added to address a complaint of "hesitation/poor throttle response" during several minutes of operation after starting a cold or warm engine at an ambient temp above 75 degrees F.
A few things on these model years because of these changes.


Second, if your car is not running right and you have questions, make sure to specifiy whether your car has had the upgrades.


Third, the external resistor may be the source of a "no run" condition, if the solder connection breaks from handling the temperature sensor connector. This resistor is usually soldered just behind the connector and may be concealed under the rubber boot. A broken or bad solder connection will mean that your car will not start or run, and this could be an intermittent problem because of engine vibration. In an emergency, you can disconnect a wire to the short 2 prong temperature sensor that feeds the idle control module, and the car will run, but the idle will surge hard. It may be better to carry a short wire with small insulated alligator clips on both ends in your tool kit to do a roadside repair.

Anyone with simple logic knew that adding a resister to the coolant wire would make the mixture just a little richer and the car would run better."


Should I leave the resistor in there? My car is an 87 but is definitely not a 270 "gold band" resistor. ...definitely the 560 ohm.