'98 E39 high cluster - Reports incorrect water temp

Hi all,

For most issues on the E39s, I've been able to read myself up to a solution on these brilliant forums. However, now theres a harder nut to break..

Its about an E39 520iaT, prod. 04/98 with the high OBC cluster.
For a long time the temperature gauge has shot into max warm when only the ignition is turned on. Also the OBC Test 7 shows 125C when engine cold. Clearly this is bogus since everything actually is ice cold in this norwegian environment.. (-5C).

When starting the engine, displayed temp will slowly rise from 125 to 138C, eventually setting off the coolant temp warning.

The cooling system has been completely overhauled for a while back and, as such, is in tip top condition with all air bled, and a new stat and housing installed etcetc.

In the end I suspected the dual temp sensor in the cyl head and replaced it today.
I was suprised to see that the problem persisted on my cluster.
BUT - when connecting diagnosis equipment, it shows that the coolant temp is 68C at the same time that the cluster says warningwarning and Test 7 displays 135C.
Thats weird, beeing that both of them draws data from the same sensor..

I'm a bit dazzled by this and beginning to suspect the cluster itself beeing knackered...
Even though everything else on it works...

Hopefully any of you can point me in the direction of a solution =)

Thanks all

The coolant temp sensor has two elements: one feeds the DME (and external diagnostic equipment), and the other feeds the cluster. That side of the sensor may be defective. Also check the connector and wiring.

Yes, I would suspect so - Therefore I tried two different new sensors with correct partno to no avail.
Weirdly enough, while there was no sensor connected at all, temp would still fluctuate between 118-125C on the cluster.

May be more information here:
- What is the temperature of the coolant & when the thermostat opens under normal conditions (1)

I am no expert in troubleshooting bogus cooling temps from the cluster or test 7, but it seems to me that you have a wiring problem (maybe a short to ground) between the sensor and the cluster. You need to identify the wire at the sensor and cluster and do some testing. The Bentley manual wiring diagrams may help.


http://www.mediafire.com/?22jnmjinyom

Just guessing! Good luck,

Do you have a friend with similar cluster so you can swap to make the diagnosis?

Originally Posted by johnstern

...
The Bentley manual wiring diagrams may help.

http://www.mediafire.com/?22jnmjinyom

Just guessing! Good luck,

Be carefull of this site.
My Norton Internet Security blocked it as a threat

I downloaded the manual onto my iPad and have had zero problems. It may be an Apple vs PC thing. I haven't tried it with my desk top, PC. I have the paper manual anyway but thought it might be useful on the iPad.

Thanks for the warning, rdl.

Thanks everyone for your answers.
I'd absolutely want to swap a mates cluster to rule it out, but sadly noone has got one.

Gonna try measuring the wire from the sensor to the cluster, and possibly just snip it and draw a new one if this turns out to be the prob. If not - It may point to the cluster itself.

But is it only me or is actually the whole Chapter 6 Electrical system missing from the Bentley in the link? would be just my kinda luck

The download was fine, I guess mediafire.com may be somewhat questionable - But it should be fine as long as you can trust the file youre downloading.

/D

Here's another place for wiring diagram info if you need it....

http://www.bmw-planet.com/diagrams/release/en/index.htm

Originally Posted by dannar

Yes, I would suspect so - Therefore I tried two different new sensors with correct partno to no avail.
Weirdly enough, while there was no sensor connected at all, temp would still fluctuate between 118-125C on the cluster.

Originally Posted by johnstern

I am no expert in troubleshooting bogus cooling temps from the cluster or test 7, but it seems to me that you have a wiring problem (maybe a short to ground) between the sensor and the cluster. You need to identify the wire at the sensor and cluster and do some testing. The Bentley manual wiring diagrams may help.


http://www.mediafire.com/?22jnmjinyom

Just guessing! Good luck,

I am very inclined to agree with the short somwhere.

The dual temp sensor is in the back of the engine and a tad hard to access, certain "moves" to pull it out and replace might needing to be done by feel rather than seeing everything.

Just go back with some mirrors and lights, and inspect the wiring that goes to the connector. It might be frayed due to heat cycling, and if you can trace the wire all the way back, especially where it's close to the engine. I know it's wrapped. Also, do the same check at the front, where the other temp sensor is. The engine has cold/hot cycles and vibrations. The cluster less so.

Appreciate all your answers, guys.

It's taken me awhile to research this issue further, its darn cold outside..

So Ive ohm measured the wiring from the dual temp sensor between the sensor itself, the electrics box under the passenger side airbox, and between the elbox into the cluster.
As far as I can see it all checks out OK. Measured the values of the sensor and observed the same values in the other end of the wiring.

So I continued by snipping off the BR/VI and BR/GE wires, which is supposed to (and confirmed by measuring) to come from the temp sensor - with the blue connector plugged in- and a value of around 110 C remains on the cluster. BUT with the blue connector UNplugged, it says -128 - no connection to sensor. So I tried drawing two new wires from the sensor into the cluster on the two pins of the original wires ( Pin 18 and 19 on the blue connector) with the blue connector still UNplugged - Still -128.

last thing I tested was measuring the pins on the cluster itself. Tried it with the blue connector in place, and while OHMing the pins (I hacked into the wires) I observed that the temp went down by many degrees while the OHMmeter was conencted.

So I'm now leaning against the though of a dodgy cluster..
Almost like there is a power leak of some kind related to the blue connector.

So I'm now leaning against the though of a dodgy cluster..
Almost like there is a power leak of some kind related to the blue connector.

Unfortunately, I think you're correct.

What surprised me is you have a high cluster and your car year is a 98, this is going to be harder to find one on Ebay.

I find it kind of weird that only the temp gauge has a problem while everything else on it is good. Could it be that the cluster can be coded to draw its coolant temp from the i-bus og can bus or even from the DME instead of the analog line?

If noone has any more suggestions to this, I think the next step will be to slap in a new cluster.

Here in Europe its actually pretty easy to get a hold of these using the german version of ebay. Even with identical partno, in the jungle of cluster P/Ns..

Coolant temperature display

Since 5/97 an instrument cluster has been phased-in which features the plugged-on instrument cluster electronics (IKE) integrated in the display unit (AE). This instrument cluster can replace older instrument cluster versions.

The instrument cluster determines the current coolant temperature from the coolant temperature sensor (NTC resistor). The coolant temperature sensor is connected by means of its own ground (analog ground) and sensor line (analog positive) to the instrument cluster electronics (IKE).

In the case of the integrated version of the instrument cluster, phased-in as from 5/97, the coding data defines whether the coolant temperature signal is routed via the CAN bus from the engine control unit or via a separate line from the coolant temperature sensor to the instrument cluster.

The instrument cluster electronics (IKE ) transfers the "coolant temperature" information via the instrument bus (I-bus ) and body bus (K-bus).

So you might have the engine variant where the coolant temperature signal is read on the CAN bus by the instrument cluster.

Hi all.
I'll conclude this thread just for future reference..
My cluster was effed. Got a used one off of german Ebay for no more than roundabout $90 - with bad pixels. So I did the pixelfix, reset and recoded the new cluster, and everything is 100% back to normal.
Thank you all for helping.

Originally Posted by dannar

Hi all.
I'll conclude this thread just for future reference..
My cluster was effed. Got a used one off of german Ebay for no more than roundabout $90 - with bad pixels. So I did the pixelfix, reset and recoded the new cluster, and everything is 100% back to normal.
Thank you all for helping.

Good work and thanks for the update. Happy motoring

Thanks for the update.

Here's a graphic I made for another thread, which is related and so it may help someone in the future.

Originally Posted by bluebee

I recognize the photo in the original post as being my cluster (see How to replace Double Temperature Switch BMW E39 525i) so I know the OP has seen at least some of what I write below.
But, just in case others need the information, two good threads spring to mind to better understand the cooling system measurement:

Typing /thermostat F3 in the bestlink thread finds this one on how the gauge tracks temperature:
- What is the temperature of the coolant & when the thermostat opens under normal conditions (1)

And, typing /dts F3 finds how to 'trick' the cluster into reading each of the dual temperature sensor values:
- How to replace the M54 dual temperature sensor (DTS, aka double temperature switch) in the M54 (1) (2) (3) (4) & how to make your own short DTS removal tool out of a 22mm or 7/8" box wrench (1)