Cruise Control Issue Question

[Boaring1961]

My cruise will occasionally stop working on long road trips. It'll disengage while cruising at 70 mph and then when I reset it it'll engage, but in 30 secs to a couple of minutes later it'll disengage again. It'll do this for 3-6 times over a 10 minute period and will then start working fine again for the rest of the trip.



Thoughts? Does my truck have a vacuum pump? Servo issue? I don't have a clue where to even look.

 

[JLandry]

Could it be a misadjusted brake lamp switch?



If the brake lamp switch is being triggered, then the cruise control will disengage.



John L.

 

[cerberusiam]

No vacuum pump, the CC is all done in the ECU. Brake switch would be a good place to start.

 

[Boaring1961]

How does one go about adjusting the brake switch?

 

[JLandry]

How does one go about adjusting the brake switch?

According to the factory service manual, the brake lamp switch has a one-time adjustment feature when first installed. It can't be readjusted later and must be replaced if not working correctly.

To check the switch function, with the engine running, I'd simply have someone watch the brake lamps (or back the truck up to a wall after dusk so you can observe the brake lamp output yourself) while you gently press and wiggle the brake pedal. If the switch seems overly sensitive, that is the brake lamps are illuminating with barely any movement of the brake pedal, then you'll need to replace the switch.

Here are the removal and installation instructions from the factory service manual:

Removal

1. Disconnect and isolate the battery negative cable.

2. Locate the brake lamp switch (1) near the support bracket on the lower steering column (3).

3. Disconnect the wire harness connector (5) from the brake lamp switch.

4. Rotate the brake lamp switch housing clockwise about 30 degrees to align the tabs on the switch locking collar with the keyed hole in the switch mounting bracket (4).

5. Pull the switch straight back from the keyed hole to remove it from the bracket.

CAUTION: The brake lamp switch self-adjusting switch plunger is a one time only feature. If the switch is removed from the mounting bracket, it MUST be replaced with a new switch.

6. Discard the removed brake lamp switch.​

Installation

CAUTION: The brake lamp switch self-adjusting switch plunger is a one time only feature. If the switch is removed from the mounting bracket, it MUST be replaced with a new switch.

1. Depress and hold the brake pedal in the depressed position.

2. Align the tabs on the brake lamp switch locking col- lar with the keyed hole in the switch mounting bracket (4) on the lower steering column (3).

3. Insert the tabs on the brake lamp switch locking collar through the keyed hole in the switch mounting bracket until the switch housing (1) is firmly seated against the bracket.

4. Rotate the switch housing counterclockwise about 30 degrees to engage the tabs on the locking collar with the switch mounting bracket.

CAUTION: Do not release or pull up on the brake pedal before the switch plunger adjustment has been completed.

5. Release the brake pedal, but do not pull it upward.

6. Rotate the plunger adjustment release lever (2) clockwise until it locks into place. The lever should be parallel to the brake lamp switch connector receptacle. This action will set the switch plunger length to a final adjustment position and cannot be undone. If not performed properly the first time, a new brake lamp switch must be installed.

7. Reconnect the wire harness connector (5) to the brake lamp switch.​

 

[Boaring1961]

Good info thanks!!

 

[hcole]

Boring, it does sound like it might be your brake switch. I have a way you can check it without going to the trouble to adjust it. Just take a weak screen door spring or similar spring and attach it to the brake pedal and steering column so it pulling up on the pedal and drive it for a few days, and if it doesn't do it any more, THEN adjust it. That's what I did.

 

[AH64ID]

I would also check for any codes that may not create a CEL. A malfunctioning wheel speed sensor can do the same.

 

[Boaring1961]

Thanks for the info guys.

I can try to get a code with the key technique. I hate taking it to the dealer so I'll do what I can at home.

hcole, the only issue is that it does it so infrequently and since I work from home I don't get to run it on cruise very often. The last time this happened was in July on a 10 hr drive to scout for an upcoming elk hunting trip. I'm doing the same 10 hr drive this Wednesday evening for a second scouting trip so I'll see if it does it again.