Cruise Control Doesn't Engage

[mkIIIman089]

Hey everyone, having a bit of an issue with my CC working, and I'm hoping to get it working before I have to drive a ~1200 mile trip next week!

Problem:
Push Cruise Main, and the indicator comes up on the dash like normal, and you can hear the relay activating. However, the set/coast button does absolutely nothing, and it just refuses to "set" at any speed. This issue seems to have gradually come about, not too long ago it would work perfectly 1 time then it would be a battle to get it to engage any time after that. Previously, once it had engaged it worked perfectly!

Diag System shows that Set/Coast and Resume/accel buttons are both sending the proper signal. "Vacuum switch on" is constantly repeating itself when the buttons are not being pressed and the engine is not running. Diag mode with the engine running is where things begin to get questionable, the buttons still indicate their proper codes but aside from that (Cancel switch, and both speed sensor tests) result in no code at all - the light is "off" all the time. Also, there are no stored codes, and the indicator doesn't flash when I'm trying to get it to "set" outside of diag mode.

I tried several times to get the cancel switch and speed tests to give a result but I couldn't get anything from it. Unfortunately I don't know if I am improperly doing the tests, or if there is actually something wrong with either the speed sensor or a cancel switch is for some reason constantly "on".

I set the cable freeplay per TSRM, but I don't have a vacuum pump to manually test the actuator or the vac module on the car - I am fairly certain they are not the problem.

Lastly, does the tail light failure box have anything at all to do with the "stop light switch" circuit? I bypassed the box because of my LED bulbs, TEWD lists SW A and B for that circuit on the CC diagram - but I'm not sure what exactly it's referring to.

Input, ideas, suggestions?

 

[rayall01]

Hey everyone, having a bit of an issue with my CC working, and I'm hoping to get it working before I have to drive a ~1200 mile trip next week!

Problem:
Push Cruise Main, and the indicator comes up on the dash like normal, and you can hear the relay activating. However, the set/coast button does absolutely nothing, and it just refuses to "set" at any speed. This issue seems to have gradually come about, not too long ago it would work perfectly 1 time then it would be a battle to get it to engage any time after that. Previously, once it had engaged it worked perfectly!

Diag System shows that Set/Coast and Resume/accel buttons are both sending the proper signal. "Vacuum switch on" is constantly repeating itself when the buttons are not being pressed and the engine is not running. Diag mode with the engine running is where things begin to get questionable, the buttons still indicate their proper codes but aside from that (Cancel switch, and both speed sensor tests) result in no code at all - the light is "off" all the time. Also, there are no stored codes, and the indicator doesn't flash when I'm trying to get it to "set" outside of diag mode.

I tried several times to get the cancel switch and speed tests to give a result but I couldn't get anything from it. Unfortunately I don't know if I am improperly doing the tests, or if there is actually something wrong with either the speed sensor or a cancel switch is for some reason constantly "on".

I set the cable freeplay per TSRM, but I don't have a vacuum pump to manually test the actuator or the vac module on the car - I am fairly certain they are not the problem.

Lastly, does the tail light failure box have anything at all to do with the "stop light switch" circuit? I bypassed the box because of my LED bulbs, TEWD lists SW A and B for that circuit on the CC diagram - but I'm not sure what exactly it's referring to.

Input, ideas, suggestions?

Did the problem start just after you bypassed the tail light sensor?

 

[mkIIIman089]

I can't be sure of the exact timeline, but I can definitely say it was intermittent before I bypassed it. I have been driving so little now, I can't be sure when it completely stopped working.

 

[rayall01]

What codes do you have? I know some codes will disable the CC, but I can't remember which ones.

 

[mkIIIman089]

No codes.

 

[Nocheez]

Is the "BRAKE" light on the dash on? If so, cruise will not engage.

 

[mkIIIman089]

Nope, no brake light either.

 

[Nocheez]

Nope, no brake light either.

OK, if you're sending the right signals from the switch and they are being received by the cruise control box, then we've got to assume that something is happening with the box that won't allow cruise to engage.

It could be a faulty cruise box, but I'm thinking something else is causing it to cancel. Are you 5-speed? The clutch pedal switch might be sticking and the car thinks the clutch pedal is being depressed (not the sad way) and won't allow it to engage. It could also be something from the lamp failure box, though I'd have to check the wiring diagrams first.

 

[mkIIIman089]

Well, weirdly, the clutch switch was completely unplugged... still no CC though.

I'm certainly no pro at reading the EWD, so I can't really tell if the Tail Lamp Failure box anything to do with it. All I can really say is that things you would never expect to be related, are, when it comes to things that involve the cluster. LOL. So if you can tell whether or not it does, it'd be a step for sure!

It did work, for more than a year, with the tail light failure indicator illuminated on the dash... so why it would work when a failure is actually indicated but wouldn't work if there is no failure signal - doesn't really make much sense.

 

[Nocheez]

Well, weirdly, the clutch switch was completely unplugged... still no CC though.

I'm certainly no pro at reading the EWD, so I can't really tell if the Tail Lamp Failure box anything to do with it. All I can really say is that things you would never expect to be related, are, when it comes to things that involve the cluster. LOL. So if you can tell whether or not it does, it'd be a step for sure!

It did work, for more than a year, with the tail light failure indicator illuminated on the dash... so why it would work when a failure is actually indicated but wouldn't work if there is no failure signal - doesn't really make much sense.

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=BE&P=58

According to this, it doesn't have anything to do with it.

 

[mkIIIman089]

So, sort of back to square one then...

Thinking out loud: There should be an EFI code 42 if there were something wrong with the speed sensor signal, just checked again for kicks and there are no codes present.

 

[RazoE]

is your speedo working properly..?

does it wobble..?

faulty speedo will do that as well, it'll cut the CC..

 

[GrimJack]

Most common causes for dead CC:
- Speedo cable
- Cancel switches on the brake / clutch pedal out of adjustment

 

[mkIIIman089]

Speedometer is solid as a rock at speed, and I have seen wobbly speedometers that do allow the cruise control to continue working - although not quite as accurately as it should.

It isn't being killed, it just isn't engaging.

I'd like to see what results others get from running "Type A" codes on their car, to see how their diag system behaves on the cancel and speed tests.

The brake switch also operates the tail lights, and they work fine. The clutch switch up until just now apparently wasn't even plugged in, and plugging it in made no difference. Also, it looks like the off position is "open" for the clutch, eliminating that as the problem.

I'll go and check "SW A" on the brake pedal switch just to be sure both switches are working.

*UPDATE* Checked the brake switch, it's functioning normally on both sets of terminals.

*UPDATE 2* Checked the clutch switch, it's also working properly.

*YET ANOTEHR ONE* Checked the vacuum pump, builds and holds vac perfectly. Checked the actuator the best I could, with voltage and vacuum it will pull the cable, but it definitely doesn't hold any vacuum when powered up. It just returns to it's rest position unless you constantly pump it. Vacuum switch tested OK.

Also, just did some volt meter checking at the computer connector. The brake switch is working as it should, the clutch switch goes from 7000 ohms to 30 ohms... not exactly ideal, but a drastic change between pressed and released. Pressing the cancel button results in a proper signal as well.

IDK what else there is to test...

 

[mkIIIman089]

Well, to sum it one and give one last "bump":

Mechanical checks:
Vacuum pump - OK
Actuator - OK
Vacuum Switch - OK
Clutch button - OK
Brake button - OK

Electric checks (Measured at CCS Computer connector):
Stop Fuse - OK
Stop Light Switch - OK
Release Valve/Stop Light switch - OK
Control Valve - OK
Main Relay - OK
Indicator - OK
Set, Resume, Cancel buttons - OK
Speed Sensor - OK
Clutch switch signal - 30 Ohms pedal pushed in, 7k ohms pedal released
Parking brake switch signal - OK
Vac switch signal - OK
Vac pump signal - OK
Body ground - OK

So, apart from starting to throw parts at it (since I don't see a way to test the CCS Computer itself) I'm stumped on this one...

 

[Nocheez]

I vote that you try another CCS computer and go from there. Any Supra owners near you that can let you borrow theirs? It's really easy to get out from under the dash.

 

[mkIIIman089]

Yea, I saw it up under there (obviously) when I took the connector off to check it's getting all the right signals.

Unfortunately it's not quite as easy as that may first seem. LOL. I've found that most people are perfectly okay with having broken cruise control, or think it's cool to not have it. Compound that with the fact I need one from a turbo within the ~2 year production span (88240-14180) AND know that it is actually working... but I can always try!

 

[Kristian_Wraae]

My cruise control started to fail a few months after I bought my car. The weather and temperatur had great influence on whether it would work or not. Usually the on/off button would work but the set speed never worked.

The problem turned out to be the slipring underneeth the steering wheel that conducts the signals from the buttons.

Tried to clean the connectors which worked for two weeks then the same problem. Bought a new slipring from Toyota and it has worked since. Took about one hour to replace it.

 

[mkIIIman089]

My buttons no longer go through the steering column and are hard wired to a different location because of my aftermarket steering wheel. Plus the CCS computer does recognize when they are being pushed and all of them are outputting within 2 ohms of their specified resistance values at the computer connector.

Similar symptom though, for sure. Mine just seemed to go from perfect, to bad, to dead though. LOL.

 

[mkIIIman089]

Finally got around to trying a couple different ECUs, one was clearly fucked, but the other passed the diag checks fine and presented with the same problem. So, I'm at a loss again, I may re-install the tail light failure box for shits and giggles at some point but right now I think I may be done with trying to solve this one.