cruise control - obc not updating

[89_525i_PhoenixAZ]

Hi everyone. I have a 89 525i m20 and I have been searching for weeks now to a solution for my cruise control not working. My speedometer, tach and gauges seem to be working fine. Also, the OBC temp gauge seems to work fine after first driving the car for a little bit and then it seems to freeze on the last temperature it was on along with the distance till empty gauge freezing too. The MPG and MPH screen just shows a "---MPH" and "---MPG". I did swap the cruise control actuator with no change. Has anyone here experienced this problem before or does anyone know of any solutions to the problems I am having? I have been racking my brain trying to figure this out. Any help will be greatly appreciated!

[mikell]

Did you check the the safety cut out switch(s)? Most often that is the culprit - or at least the easiest to fix.

[billy]

so is this related to cruise control, ie does this only happen when cruise control is activated?
and when the obc says ---mph i take it that the actual needle speedo is still working?
it is strange that the mpg should reset, because once you have a reading, subsequent readings are then averaged out - for it to say --- seems to suggest that the OBC has reset.

Once this situation occurs, how do you reset it - just restart the car?

im thinking its an obc fault, however if it only occurs when you have cruise activated then perhaps the cruise control ecu is causing some sort of crash

[billy]

Did you check the the safety cut out switch(s)? Most often that is the culprit - or at least the easiest to fix.

whats a safety cut out? do you mean the crash sensor or fusible link?

the fusible lnk is a theory as it could be causing a break and resetting the obc - however i think you would see many other problems if this was the case

[89_525i_PhoenixAZ]

my cruise doesn't activate at all and yes the speedo is working fine. What are you referring to when you say "safety cut-off switch"?

[mikell]

The brake light switch also disables the cruise when the brakes are applied. The contacts sometimes get pitted and the cruise will cut out. Switch replacement is pretty easy. Manual cars also have a switch on the clutch. See bmwe34.net I think Bruno has a write up on the switch replacement.

[attack eagle]

and automatics use the gear indicator reader on the shifter, as well as speedo input to prevent it activating in neutral,or if speed is too low.

[89_525i_PhoenixAZ]

well I fixed the problem. I swapped out the instrument cluster with a spare I have from a parts car and problem solved. Everything is working now. I just need to figure out to get rid of the S P on the display because the cluster came from a 92 525i that has sport shift auto or whatever you call it and my 89 does not have it. Thanks everyone for your help, what a relief after 3 weeks of checking cables and such...

[attack eagle]

if it is a manual, you just take the bulb out. mine times out after 10-15 seconds and the display goes fully black.

[billy]

well I fixed the problem. I swapped out the instrument cluster with a spare I have from a parts car and problem solved. Everything is working now. I just need to figure out to get rid of the S P on the display because the cluster came from a 92 525i that has sport shift auto or whatever you call it and my 89 does not have it. Thanks everyone for your help, what a relief after 3 weeks of checking cables and such...

Thats related to the coding plug, have you swapped them?

the 89 coding plug maybe built into the loom, it depends but on the new cluster the plug is in the back of the cluster itself and this tells the cluster what type of gearbox you have and wether to illuminate the gearbox lcd selection, it also stores the cars mileage and fuel tank size etc etc

[89_525i_PhoenixAZ]

yeah, my coding plug is on the back of the cluster but my original cluster backing was white and the new one is blue. Can I have the coding plug reprogramed to match the settings for my car?