All possible cruise control problems?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by flapjackthekandikid, Aug 18, 2019.

  1. flapjackthekandikid

    flapjackthekandikid Junior Member

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    I have a 2008 prius and the cruise control has not worked for some time (about a year or two, maybe longer). The light will come on, blink once, and then go off. The cruise control never engages. Occasionally I can get it to engage for a few seconds before it disengages. I had a load of repairs done last week from my super reliable guy a few hours away that does all the repairs almost at-cost for me. He repaired a cylinder misfire I had gotten diagnosed from pepboys by reading their diagnostic readout code and googling it, along with my brights that hadn't worked for a few weeks (I believe I just installed my new headlight bulbs while the brights were engaged so it couldn't disengage), but after replacing the coil behind the steering wheel horn about 4 times, we determined it couldn't be that. There were no other error codes on the diagnostic after replacing the coil, just old ones that had been fixed; but the cruise control still gave me the same trouble. What are all the possible causes for cruise control acting like this and not being able to engage? I'm headed back on tuesday to check it out and we're going to run every possible test to see what is up, but if I have a stepping-off point of the secondary most common problems to address, it might make the process faster and we can identify and fix the problem easier.
     
  2. fuzzy1

    fuzzy1 Senior Member

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    I don't have anywhere near a complete list, but two easy potential issues would be:

    * driving in B mode instead of D;
    * brake light switch not working or not properly mechanically engaged to brake pedal arm.

    For the later, are your brake lights working? If not, that and cruise control could be linked to the same switch.
     
    #2 fuzzy1, Aug 18, 2019
    Last edited: Aug 18, 2019
  3. Elektroingenieur

    Elektroingenieur Senior Member

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    The Repair Manual (more info) has a Problem Symptoms Table, under Cruise Control System, that lists the most common causes. As @fuzzy1 kindly mentions, it could be a problem with the stop light switch circuit—though this wouldn’t necessarily cause a problem with the brake lights, too—or with the cruise control switch circuit. There are other possible causes listed there and in the Fail Safe Chart.

    For fastest diagnosis, I’d suggest using the Data List feature of a Toyota Techstream diagnostic system, which can show the status of the inputs to the Hybrid Vehicle Control ECU, including both of these circuits, in real time. You can try each switch in turn and see if the ECU is getting the signal; if not, you’ll know where to start checking the switches, wiring, and connectors.
     
  4. flapjackthekandikid

    flapjackthekandikid Junior Member

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    Hey it's been about a year since I had this problem, but figured I'd followup for anyone else that might run into this with no solution! We replaced the actuator and it wasn't that, and tried messing around more with the steering spindle to see if it was anything around that; as well as electrical; but I noticed one day that whenever I held my brake lever upwards with my foot wedged underneath it, my cruise control would work. My mechanic tightened my brake pedal up a bit higher to see if I'd have any difference, and we figured out that the pads kept engaging while I was driving making the car think that I was braking and disengaging or not even allowing the cruise control to engage the entire time. We fixed this about a year ago and I haven't had cruise control problems whatsoever since. Worth a shot to anyone having a similar issue
     
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  5. ChapmanF

    ChapmanF Senior Member

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    It doesn't have to have been pads actually engaging, as the only thing the cruise system cares about is the electrical switch directly above the brake pedal. Seems like your pedal height did not match the adjustment of that switch.

    The diagnostic steps Elektroingenieur kindly suggested in #3 would readily reveal such a cause.
     
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