Automatic Transmission Shift Lock Control System
With the ignition in the ON position, voltage is supplied to automatic transmission shift lock control switch. Voltage flows through the normally closed contacts of the automatic transmission shift lock control switch to the automatic transmission shift lock control solenoid. The automatic transmission shift lock control solenoid is permanently grounded. This energizes the automatic transmission shift lock control solenoid causing the transmission shift lever to be physically locked in the PARK position. When the brake pedal is pressed the contacts in the automatic transmission shift lock control switch open, de-energizing the automatic transmission shift lock control solenoid. This allows the shift lever to be move out of the PARK position.
The automatic transmission shift lock control system is a safety device that prevents an inadvertent shift out of PARK when the engine is running. The driver must press the brake pedal before moving the shift lever out of the PARK position. The system consists of the following components:
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The automatic transmission shift lock control solenoid
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The automatic transmission shift lock control switch
Shift Lever Does Not Move with Brake Pedal Depressed ?
2
Does the shift lever move out of the PARK position?
Go to Testing for Intermittent Conditions and Poor Connections
Go to Step 3
3
Does the shift lever move out of the PARK position?
Go to Step 7
Go to Step 4
4
Does the test lamp illuminate?
5
Does the test lamp illuminate?
Go to Step 6
Go to Step 9
6
Does the test lamp illuminate?
Go to Step 8
Go to Step 11
7
Inspect for poor connections at the harness connector of the automatic transmission shift lock control switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 14
Go to Step 13
8
Inspect for poor connections at the harness connector of the park lock/automatic transmission shift lock control solenoid assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 14
Go to Step 12
9
Repair the open or high resistance in the park lock solenoid ignition 1 voltage circuit. Refer to Circuit Testing or Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 14
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10
Repair short to battery positive voltage in the A/T shift lock control solenoid supply voltage circuit. Refer to Circuit Testing or Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 14
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11
Repair the open or high resistance in the park lock solenoid ground circuit. Refer to Circuit Testing or Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 14
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12
Important: Depress the button on the side of the shift lock actuator. With the button is depressed, cycle the plastic straw within the shift lever 3 to 5 times. The straw should move smoothly and freely except near the top of the travel where additional force will be required to mechanically actuate the park lock mechanism inside of the shift lock actuator. If there is stick/slip or abnormal friction while cycling the plastic straw or if the straw is altogether stuck in the lever, the entire control assembly (shifter and shift lock actuator) needs to be replaced. Refer to Transmission Control Replacement . If there is no abnormal friction, replace the shift lock actuator. Refer to Automatic Transmission Shift Lock Control Actuator Replacement .
Did you complete the replacement?
Go to Step 14
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13
Replace the automatic transmission shift lock control switch. Refer to Stop Lamp Switch Replacement in Lighting Systems.
Did you complete the replacement?
Go to Step 14
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14
Operate the system in order to verify the repair.
Did you correct the condition?
System OK
Go to Step 2
SOURCE: How to replace the headlights on my 2003 GMC envoy.
The headlights on the envoy are the easiest parts of the car to repair. You just pull the two tabs at the top of the headlights, screw out the bulb containers and you are good to go
SOURCE: how do you change brakes on a 2003 gmc envoy
don't need any special tools, standard sockets sets, "C" clams is a must unless your a He-Man and wrench set, plyer or needle nose will do. I assumed being 2003 your rotor never have been turn and i recommend every time you change your bakes is good idea to have your rotor turn. reason is it will make your pad last lot longer, removed any vibration and better even wear on the pad and eliminate any squealing although is not necessary to do so. make sure you get extra break fluid to bleed the brakes. get your self 5 feet long smallest vacum rubber hoses and a glass jar to bleed your brake fluid in. the rubber vacum hose you going to use to fit on to the bleeding nipple and run the other end of line to your the glass jar to save the brake fluid when you bleed the brakes. when removing caliper, check inspect make sure the rubber seals around your piston look good and not crack or deteriorated. before applying new pad make sure you open the bleed valve to reduce the pressure by turning the bleed nipple counter clockwise and leave it open attach that rubber hoses to the nipple because you going to press on the piston back into it housing with the "C" clamp in order for new pad to fit. becareful not to damage the rubber seals around the piston. its going to take lots of effort to push that piston back in so be a bare with it if needs to. once the pad is back in make sure you keep the reservoir full with brake fluid and then bleed the brake. two people is a good idea to do brake. one will do the pumping the brake and holding it down and other will bleed the nipple. I bleed it 2-3 time will do the job. good luck!
SOURCE: GMC Envoy w/ code P0128
Start at $89 right off the bat just for diagnostics and then depending on what they find that is causing that fault, at LEAST one hour labor, plus parts....I would say $250 is a good ballpark figure....looking up your fault code now.
SOURCE: wont shift back from 4x4 low, to 2x2
I also have a 2002 Envoy. Shifting to and from 4wh and 4wa can be done on the fly but shifting to 4wL has to be done stoped and while in neutral. Try that. Otherwise I'm afraid its a new computer for you. Its located under the left rear seat and you need a loan for one.
SOURCE: The button on our 2004 GMC Envoy gear shift will not depress when
The brake rlease switch for the gearshift might need adjusted-replaced or the shifter itself might need adjusted
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