Cruise control turns on but won't set

[mrmeme1212]

Greetings brains trust.

As the title says my cruise control turns on fine but won't set, I've seen other posts pointing at the switches on the clutch/brake pedals but they both seem to be fine. Are there any other easy culprites we know of, or a more sure fire way of testing the switches?

Cheers,

Jay

 

[Old.Tony]

I thought my brake pedal switch was fine until I pulled it out and dismantled it (about 2 weeks ago now). Inside, a small amount of carbon buildup was present making for an erratic connection. As chance had it, every time I checked the brake lights (usually by looking at the reflection in a window somewhere or the glow on the road at night) they were working, but when the mechanic was checking them for rego, nothing! Removing the switch was very simple - disconnect the electrical connector and a quarter-turn anticlockwise had the switch in my hand.

There are other criteria that need to be met for cruise to engage. The vehicle must be travelling at 30mph (40km/h) or more (instrument cluster, unlikely to be a problem unless the earth has failed - try earthing the stereo separately). The vehicle must not be in neutral (check neutral position switch on the gearbox). The brakes cannot be engaged (second switch on the brake pedal arm). The clutch in a manual must not be engaged (switch on the pedal arm). I'd mention the handbrake but I've never tried pulling the handbrake above 40km/h to see if it disengaged my cruise - now that I'm thinking about it, I might just do that at some point soon "just to find out". Not fully engaging - only enough to engage the switch. You probably don't need to worry about this, it should light up the handbrake indicator on the instrument cluster if it thinks the handbrake is engaged.

The switches are very simple on/off switches and a simple resistance test will show whether they are working or not.

 

[mrmeme1212]

Cheers I'll pull the switches off this weekend

 

[D40-12-Xtra-Newc]

Hi,
Agreed to check the Brake (& Clutch) switches first.

On my case, same symptoms, it was an intermittent fault with the NPS (Neutral Position Switch) on the top front of the Gearbox, accessible from the top by removing the console.
Diagnosed initially by holding the Gearshift to the left, in gear, and it worked, but as soon as released, Cruise 'Un-set' itself.
Replaced with OEM part, no issues since, have done 40,000 km since.

 

[mrmeme1212]

Hi,
Agreed to check the Brake (& Clutch) switches first.

On my case, same symptoms, it was an intermittent fault with the NPS (Neutral Position Switch) on the top front of the Gearbox, accessible from the top by removing the console.
Diagnosed initially by holding the Gearshift to the left, in gear, and it worked, but as soon as released, Cruise 'Un-set' itself.
Replaced with OEM part, no issues since, have done 40,000 km since.

Just saw a video with that trick for the NPS! Will give it a go on my pilgrimage to work.

 

[Scott52]

Greetings brains trust.

As the title says my cruise control turns on fine but won't set, I've seen other posts pointing at the switches on the clutch/brake pedals but they both seem to be fine. Are there any other easy culprites we know of, or a more sure fire way of testing the switches?

Cheers,

Jay

There's a good chance it's your NPS. It's very common for the switch to wear internally meaning the contacts don't quite work. It's an easy repair.

 

[Scott52]

I have a friend with a Thai D40 2012 STX diesel manual king cab. About a year ago his CC started un-setting itself. He was going to buy a new NPS but I convinced him to save his cash and do the spot weld trick on the end of the plunger.

Since then we've been on about 8 expeditions into remote Western Australia and our modified NPS's have never missed a beat!

The plungers on new switches are about 0.75mm longer than the originals. It's either planned obsolescence or they changed the design based on NPS failure feedback.

 

[mrmeme1212]

Yeah I'll pull it off this weekend and have a gander, will update

 

[mrmeme1212]

Pulled off the NPS and tested it, works fine. Tacked on a bit of weld like shown in the video but still no go. If I just bridge the connection would that tell me if it's the problem or not?

 

[Old.Tony]

Just unplug it. My understanding is that an open circuit indicates neutral. But, there's always the chance they did things differently in some models.

 

[mrmeme1212]

Sweet, I'll give it a go.

 

[Scott52]

Just unplug it. My understanding is that an open circuit indicates neutral. But, there's always the chance they did things differently in some models.

When I checked the NPS with a multi meter the internal switch contacts are open when the plunger is pushed in and closed when it's fully protruding. So when in gear is the switch open or closed? Is the plunger being pushed or left fully protruded? If the NPS is unplugged it's the same as pushing the plunger in. For the CC to be "set" with the NPS unplugged that suggests the plunger is pushed in when a gear is selected?

 

[mrmeme1212]

I had the exact same thought process, but I don't know how the mechinism is actuated within the gear box. I suppose I can try unplugging in and bridgning it to see if either helps.

 

[Scott52]

I had the exact same thought process, but I don't know how the mechinism is actuated within the gear box. I suppose I can try unplugging in and bridgning it to see if either helps.

Yes that's what I'd do ... see if it "sets" when unplugged. If not bridge the wires at the connector and see if that allows it to "set".

You'll have to be careful if the CC does "set" either bridged or unbridged as you're telling the CC system your transmission is in gear and can be "set". If you're on cruise and knock the lever into neutral without the clutch the RPM will shoot up as the CC system tries maintain the speed.

 

[mrmeme1212]

Yes that's what I'd do ... see if it "sets" when unplugged. If not bridge the wires at the connector and see if that allows it to "set".

You'll have to be careful if the CC does "set" either bridged or unbridged as you're telling the CC system your transmission is in gear and can be "set". If you're on cruise and knock the lever into neutral without the clutch the RPM will shoot up as the CC system tries maintain the speed.

Yeah good point, I'll just use it for a diagnosis and go from there. Do we know if the the NPS is used for anything else or just for cruise control?

 

[Scott52]

When I was interrogating the wiring diagram I couldn't find anything other than CC using the NPS. Old Tony may know something.

 

[MANNING]

Im not 100% but with the NPS unplugged, if auto, the car might start ( or try ) in gear or park? .. watch that
I think it was mentioned but if your out driving and testing the cruise, If you have the speed set and knock it into neutral, watch the car doesn't rev out

 

[Old.Tony]

When I checked the NPS with a multi meter the internal switch contacts are open when the plunger is pushed in and closed when it's fully protruding. So when in gear is the switch open or closed? Is the plunger being pushed or left fully protruded? If the NPS is unplugged it's the same as pushing the plunger in. For the CC to be "set" with the NPS unplugged that suggests the plunger is pushed in when a gear is selected?

Unplugging it should make the car think it's in gear. The manual describes the test: in neutral, should have continuity (multimeter ohms test across the two wires) and anywhere except neutral it should be "open circuit". Unplugging it is electrically the same as "open circuit" so unplugging it will make the ECU think the car is in gear.

Edit: I found this information in the MT.PDF section of the manual, page MT-12.

 

[mrmeme1212]

Turns out it does work with the NPS plugged in or not, but the 'set' light does not come on. I don't think that it was working with the set light not coming on before I extended the NPS bar, I vaguely remember thinking that could be what's happening and I tested it, but I could be wrong. In any case, CC works! Thanks for your help guys

 

[Scott52]

Turns out it does work with the NPS plugged in or not, but the 'set' light does not come on. I don't think that it was working with the set light not coming on before I extended the NPS bar, I vaguely remember thinking that could be what's happening and I tested it, but I could be wrong. In any case, CC works! Thanks for your help guys

Ah well that's good news it's working now. Some models don't have a "set" light. So previously your CC was holding a cruise speed with a "set" light illuminated on the dash?

I see you have a 2007 D40 ... is it VSK or MNT?