Cruise control not working-any suggestions

[TexasZ3]

Hi everyone.
I have a 1999 2.3 (2.5) Z3 Roadster and the cruise control has never worked since purchasing it one year ago. I am now trouble shooting the problem. I have checked the fuse and it's OK. Checked rear brake lights are working, and they are, I recently replaced the third brake light as that had failed. Also can confirm that there are no LED lights in rear brake light units.

Any suggestions on what to check next?

All suggestions welcomed

Thank you

 

[Rudyrov]

The cruise control is connected to a variety of systems that will trigger it to disconnect/disengage, one of those is the clutch pedal.
Download the diagram and trace the wiring.

 

[TexasZ3]

The cruise control is connected to a variety of systems that will trigger it to disconnect/disengage, one of those is the clutch pedal.
Download the diagram and trace the wiring.

Hi Rudyrov. Should have mentioned this is an automatic gearbox

 

[Smudgemanuk]

Is your auto gearbox changing rough at all?

There is a recent thread on here where a member had a loss of cruise control and rough auto changes. It ended up being a faulty MAF.

 

[bear2020]

Is your auto gearbox changing rough at all?

There is a recent thread on here where a member had a loss of cruise control and rough auto changes. It ended up being a faulty MAF.

That was me! Yes it stopped working and I did the same checked everything electrically and when the code reader was put on it registered it as passive.
No code for the MAF being faulty, no engine light but the DME was getting no signal and the CFM was 0 so replaced the MAF. Cruise control back and gearbox issues sorted.

 

[TexasZ3]

Is your auto gearbox changing rough at all?

There is a recent thread on here where a member had a loss of cruise control and rough auto changes. It ended up being a faulty MAF.

Gearbox is changing smoothly. I have just cleaned the MAF with MAF cleaner and reinstalled it. No change.

 

[TexasZ3]

I had the gearbox completely rebuilt last year and have added about 350 miles on it with no problem. This week the check engine light came on and found error P0101 (MAF) problem and that's why I cleaned it and reinstalled it. May be time to purchase a new one but don't see how this error can stop the cruise control working?

 

[Smudgemanuk]

My guess is that the cruise relies on a stable, predictable relationship between:

• Throttle position
• Engine load
• Airflow in (via MAF)
• Vehicle speed

With faulty MAF data the engine is less sure how much fuel need to be injected to keep the engine at a steady speed.

I think the ECU can detect this faulty MAF data and it electronically stops the cruise from working as a safety measure

 

[bear2020]

My guess is that the cruise relies on a stable, predictable relationship between:

• Throttle position
• Engine load
• Airflow in (via MAF)
• Vehicle speed

With faulty MAF data the engine is less sure how much fuel need to be injected to keep the engine at a steady speed.

I think the ECU can detect this faulty MAF data and it electronically stops the cruise from working as a safety measure

The DME gets a wrong signal. If you remove the MAF it will go back to a preset setting and you might see cruise control work again - unsure of this as never tested it.

 

[TexasZ3]

The DME gets a wrong signal. If you remove the MAF it will go back to a preset setting and you might see cruise control work again - unsure of this as never tested it.

I will try this and let you know the results.