Aftermarket LED stop/tail lights prevent cruise control working. Seems the cruise has a logic input, normally held low by brake light cct, but with LEDs, it stays high. Only answer without using power resistors to simulate ''bulbs'' that I can see, is a relay with low ohms resistor on normally closed circuit to trick cruise circuit, and when stoplight switch is applied, relay energises and opens resistor circuit. Anyone got a smarter answer, using zeners or such?

I researched these codes and found the following suggestions.Has your vehicle gone into limp mode (i.e.-check engine light is on &/or vehicle isn't making its normal power output??) Check your transmission fluid with the engine warm and at idle and if it's low,fill it to the appropriate level.P0700 is normally set when the tcm detects a fault.This is a common fault code in this model.Low/dirty transmission fluid can cause two sensors inside the transmission to short out requiring you to replace them.P0571 is related to the brake/cruise control switch, which is connected to your brake pedal.This operates your brake lights and deactivates the cruise control when you step on the brake pedal to slow down/stop.Have someone verify your brake lights are working and also make sure they're not remaining on after the pedal is released as non functioning brake lights could cause an accident.If your cruise control is working,verify it is shutting off when you press the brake pedal down.If it's not shutting off,that could also be dangerous too just like no brake lights.If it's not shutting off,check the switch to make sure it hasn't been knocked loose from the pedal and check the wiring harness also to make sure it's still connected.Check any fuse for the cruise control and brake lights also.
If the transmission fluid is low and you top it off and if you correct any condition present with the cruise/brake light switch,clear the codes with a scanner or get AutoZone/Etc to do it for free to see if the codes clear and remain that way.

What's a DHS ?
Stop Lamps

The STOP LP fuse in the rear fuse block supplies battery positive voltage to the normally open stop lamp switch. When the brake pedal is pressed, the stop lamp switch contacts close and battery positive voltage is supplied to the center high mounted stop lamp (CHMSL) and the turn signal/hazard flasher module stop lamp switch signal input. In response to this input the turn signal/hazard flasher module supplies battery positive voltage to the left and right LED tail lamp assemblies. The CHMSL and left tail lamp have ground at G402. The right tail lamp has ground at G401. The stop lamps illuminate when they receive both power and ground.
es battery positive voltage to the left and right LED tail lamp assemblies. The CHMSL and left tail lamp have ground at G402. The right tail lamp has ground at G401. The stop lamps illuminate when they receive both power and ground.

check all fuses!

Ck the fuses here is the info if you already haven't.
1-Headlight washer jets
2-Turn signal flasher
3-Headlight washer, glove box light, engine bay light, instrument cluster
4-License plate lights
5-Instrument cluster, heated seats, auto trans display, outside air temp
6-Central locking system
7-ABS
8-empty
9-heated mirrors
10-empty
11-cruise control(auto trans)
12-on board diagnostic system
13-brake lights
14-interior lights
15-power windows, climate control
16-ABS, anti-slip(?)
17-heated door locks
18-right high beam
19-left high beam
20-right low beam
21-left low beam
22-tail and side marker (right)
23-tail and side marker (left)
24-wipers and washer jets
25-blower for heating/climate control
26-rear window defogger
27-empty
28-fuel pump
29-engine timing
30-sunroof
31-tail lights, cruise control, auto trans
32-engine timing
33-cig lighter
34-engine timing
35-trailer receptacle(?)
36-fog lights
37-radio
38-trunk light, central locking system
39-flashers
40-horn
41-empty
42-empty
43-heated seats

Ok there's the numbers. To figure out what the hell that means you have to look at the inside of the cover to the fuse box. left side of dash panel. Good luck.

Brake light switch? The cruise and brake lights problems are likely related. The cruise control cuts out when you press on the brakes. I had a van where the cruse wouldn't engage. Then someone pointed out my brake lights were always on. It was the switch.

Alarmingly, the speedometer needle steadily winds down from 75 mph toward 50. Just as you uncurl your feet and try to accelerate back to traffic speeds, the vehicle downshifts with a lurch and abruptly climbs back to over 80 mph. So you tap the brakes and disengage the cruise control to avoid a conversation with one of the many law enforcement officers lurking behind every other billboard. Toggling the Resume switch settles things down, holding to a legal speed on both the uphill and downhill sections of the interstate. The kids in the back seat have stopped threatening to throw up, too. Then you look in your mirror 20 miles later and see the lights. Red and blue flashing lights. You're doing over 85 mph and, odds are, Smokey isn't going to believe you have the cruise set to 70. Time to find out why your cruise control has a mind of its own.
IT'S NOT A BUG, IT'S A FEATURE
Does your cruise control fall out of engagement partway up steep hills? Actually, it will normally drop out if the engine has to work too hard, mainly because after a while there isn't enough vacuum left to pull in the servo after sustained near-wide-open-throttle. You'll just have to put your foot into it. Downshifting helps. Do you have to ride the brakes on longer downhills to keep from building up excess speed? That's normal too. The cruise control only has authority to reduce engine speed to idle. It doesn't activate the brakes. Modern cars, in an attempt to improve mileage, have very tall gear ratios, low-friction engine designs, low-rolling-resistance tires and optimized aerodynamics. That long downgrade outside of town may have accelerated your '60s-era Pontiac to only a couple of miles per hour above legal. But, it may well propel your new economy car to blatantly ******* velocities unless you intervene by braking or downshifting. Does the Cruise icon on the dash light up when you turn the switch on? Duh. Check the fuse. You may need to look in the owner's manual to see which one if it's not tagged on the fuse box cover. An aftermarket cruise may have an inline fuse holder in the wiring to the controller.
If there is power to the system, the next check is the brake lights. Brake lights? Yup, cruise controls have a switch to toggle them off when you touch the brake pedal, and many use the same switch as the brake lights. If one of the brake lights has failed, the cruise control thinks the brakes are on all the time and won't come on. Same result if the switch is incorrectly adjusted or broken or jammed. Wait, there's more--if your vehicle has a manual transmission, there's a similar switch on the clutch pedal. You may need to break out a test light or multimeter to verify the function of this array of switches. These switches usually are normally closed switches, and close their contacts when the pedal is depressed. We've seen several cases of intermittent cruise control dropout caused by a brake light switch that was adjusted very tight. Any small bump would jiggle the brake pedal down far enough to toggle the brake lights on for a brief instant--long enough to shut down the cruise. Adjusting the switch to specs (usually so the brake lights come on after the pedal travels 1/2 in.) fixed it.

The first thing to check is the tail lights. The cruise control will not work if any lights are out. Changing to LED tail lights also causes the cruise to not work.

I suggest to check your tail lights. sometimes if they go out, the cruise control will not work. Oh and also, what i did when this happened to me, I checked under the brake pedal and pushed and pulled the little button that activates the taillights and it worked again. It may have gotten stuck..
The brake light fuse may have popped..

ALSO: -- There seems to be a recall for this..
CERTAIN PICKUP TRUCKS MAY EXPERIENCE THE PERMANENT LOSS OF BRAKE LAMP FUNCTION OR BRAKE LAMPS THAT ARE ILLUMINATED AT ALL TIMES. THE CENTER HIGH-MOUNTED STOP LAMP (CHMSL) IS AFFECTED IN BOTH INSTANCES. ALSO, IF EQUIPPED, THE CRUISE CONTROL WILL BECOME INOPERATIVE. ANY TRAILER BRAKE LAMPS WHICH ARE CONNECTED TO THE VEHICLE'S BRAKE LAMP WIRING WILL MIMIC THE VEHICLE'S BRAKE LAMPS WHEN EITHER CONDITION OCCURS.

It is not a resistance problem. As it operates normally, the cruise control is wired to the stop lamps and will operate only when it sees chassis ground through the stop lamps. When you tap your brake pedal, 12 volts is applied, the ground goes away and cruise is deactivated. Because the LED tails are diodes and only let current flow one way, the cruise cannot see ground and will not set or operate. The same symtoms would appear if you had original incandescent tail lamps and both brake lights were burned out.
The solution will be finding the wire from the cruise that senses the brake lights, and connecting it directly to the brake switch, IF the brake switch is grounded when the pedal is not pressed. You may have a relay wired to the brake pedal switch to make this happen. Seek a knowledeable car audio/accesory shop familiar with auto electrical to help you with this.
Good luck!

Start with the simple and check the fuses and the Stop lamp switch. Check your brake lights, if they're not working, the cruise won't work either. If they're not working, check the fuse for them, if the fuse is fine, then take it into the dealer, there's been a recall issued on the brake switch, so it should get fixed for free.
Cruise Control Disengaged
The powertrain control module (PCM) disengages the cruise control operation based on the signals from the following switches:

* The stop lamp switch
* The TCC brake/cruise release switch
* The clutch release switch, if equipped
* The cruise control On/Off switch

The TCC brake/cruise release switch and the stop lamp switch are mounted on the brake pedal bracket. When the brake pedal is applied, the normally closed TCC brake/cruise release switch opens and the normally open stop lamp switch closes. The PCM detects a low signal voltage on the TCC brake/cruise release switch signal circuit and a high signal voltage on the stop lamp switch signal circuit. When the clutch pedal is applied, the normally closed clutch release switch opens and the PCM detects zero voltage on the CCP switch signal circuit. The vehicle speed stored in the memory of the PCM will be erased when the cruise control On/Off button is turned OFF, or the ignition switch is turned OFF.

The Cruise Control System will disengage when the PCM detects that a driver override function has been active for approximately 60 seconds .

When the Cruise Control System is disengaged, the PCM sends a class 2 message to the instrument panel cluster (IPC) in order to deactivate the cruise control indicator.

Cruise Control Inhibited
The powertrain control module (PCM) inhibits the cruise control operation when any of the following conditions exist:

* A cruise control related DTC has been set.
* The vehicle speed is less than 40.2 km/h (25 mph) .
* The vehicle is in PARK, REVERSE, NEUTRAL, or 1st gear.
* The engine RPM is too low.
* The engine RPM is too high, with fuel cut off.
* The vehicle speed is too high, with fuel cut off.
* The system voltage is not between 9 volts and 16 volts .
* The Traction Control System (TCS) is active for more than 2 seconds .
Thank you for using Fixya and start with replacing the stop lamp switch. Even though the brake light work, it;s been known for that switch to cause your issue. that's way there was a recall for it.