Dec 082016
 

2007 GMC SierraKeep getting a ‘stabiliTrak service and service traction’ error message. The ‘brake pedal sensor switch’ has been replaced and now the message appears only when the engine is idling for more than a few minutes (disappears once I start driving). What could cause the message to keep appearing?


RESPONSE

My first guess would be a faulty sensor or sensor connection. However some hands on testing would be needed to locate the issue.

This vehicle is equipped with a BOSCH ABS/EBD/TCS/VSES brake system. The electronic brake control module (EBCM) and the brake pressure modulator valve (BPMV) is serviced separately. The BPMV uses a 4 circuit configuration to control hydraulic pressure to each wheel independently.

The following vehicle performance enhancement systems are provided.

    • Electronic Brake Distribution (EBD)
    • Power Brake Booster Solenoid Vacuum Supply
    • Traction Control System (TCS)
    • Vehicle Stability Enhancement System (VSES)

StabiliTrak® Indicator Light

Stabilitrak LightIf equipped, this warning light should come on briefly when the engine is started.

If the warning light does not come on then, have it fixed so it will be ready to warn you if there is a problem. If it stays on, or comes on when you are driving, there may be a problem with your StabiliTrak® system and your vehicle may need service. When this warning light is on, the system is off and will not limit wheel spin. Adjust your driving accordingly.

This light will also flash when the StabiliTrak® system is active.

If the StabiliTrak® system warning light comes on and stays on for an extended period of time when the system is turned on, your vehicle needs service.

Service StabiliTrak Message

 The message center displays the service stability system message when any one of many VSES-disabling DTCs is set. The EBCM sends a serial data message to the IPC requesting this display.

Service Traction Control Message

 The message center displays the service traction control system message when any one of many traction control – disabling DTCs is set. The EBCM sends a serial data message to the IPC requesting this display.

StabiliTrak Off Message

 The message center displays the stabiliTrak off message when one or more of the following conditions exists.
    • The transfer case is shifted into 4 LO. The EBCM sends a serial data message to the IPC requesting illumination.
    • The driver manually disables the VSES and engine torque reduction by pressing the traction control switch. The EBCM sends a serial data message to the IPC requesting illumination.
    • The estimated temperature of any solenoid coil exceeds an acceptable limit. The EBCM sends a serial data message to the IPC requesting this display.
    • The EBCM detects a failed brake switch. The EBCM sends a serial data message to the IPC requesting this display. A DTC sets when this condition exists.
    • VSES sensor initialization time is excessive. The EBCM sends a serial data message to the IPC requesting this display.
    • Serial data communication between the EBCM and any of several other control modules is interrupted. The EBCM sends a serial data message to the IPC requesting this display or the IPC displays the message when communication with the EBCM is interrupted.
    • The PCM is not able to perform engine torque reduction. The EBCM sends a GMLAN message to the IPC requesting this display. DTCs set when this condition exists.
    • The EBCM detects an excessively low or excessively high ignition voltage. The EBCM sends a GMLAN message to the IPC requesting this display.

Vehicle Stability Enhancement System (VSES)

 Vehicle stability enhancement system (VSES) provides added stability during aggressive maneuvers. Yaw rate is the rate of rotation about the vehicle’s vertical axis. The VSES is activated when the electronic brake control module (EBCM) determines that the desired yaw rate does not match the actual yaw rate as measured by the yaw rate sensor.

The desired yaw rate is calculated by the EBCM using, primarily, the following inputs.

    • The position of the steering wheel
    • The speed of the vehicle
    • The lateral, or sideways acceleration of the vehicle

The difference between the desired yaw rate and the actual yaw rate is the yaw rate error, which is a measurement of oversteer or understeer. When a yaw rate error is detected, the EBCM attempts to correct the vehicle’s yaw motion by applying brake pressure to one or more of the wheels. The amount of brake pressure which is applied varies, depending on the correction required. The engine torque may be reduced also, if it is necessary to slow the vehicle while maintaining stability.

VSES activations generally occur in turns during aggressive driving. When braking during VSES activation, the pedal may pulsate. The brake pedal pulsates at a higher frequency during VSES activation than during ABS activation.

VSES Sensors Initialization

 The vehicle stability enhancement system (VSES) sensors values may vary slightly due to differences in temperature, sensor mounting, connector resistances, manufacturing, etc. Since VSES is a very sensitive and precise control system, it is imperative that the electronic brake control module (EBCM) be able to accurately equate a given sensor voltage with an actual unit of measurement. For example, the yaw rate signal of one vehicle may be 2.64 volts at +18.0 deg/sec yaw rate while the yaw rate signal of another vehicle may be 2.64 volts at +17.5 deg/sec yaw rate. Therefore, at the beginning of each ignition cycle, the EBCM must perform an initialization procedure to observe how the VSES sensors are correlated with each other and also to determine what each sensor value is when the applicable unit of measurement equals 0. This voltage is referred to as the sensor bias voltage. Although some activation of the VSES system may occur if required to prior to full initialization, the system does not give optimum performance until the sensors are fully initialized.

The following VSES sensors require initialization:

    • The yaw rate sensor
    • The lateral accelerometer
    • The master cylinder pressure sensor
    • The steering wheel position sensor

When the vehicle speed is greater than 25 km/h (15 mph), full sensor initialization must occur during 3 km (1.8 mi) of driving or 1 km (0.6 mi) of straight and stable driving, whichever occurs first. Although an attempt at initialization may fail due to driving conditions, such as driving on a very winding road, failed initialization is usually caused by a sensor bias voltage which is not within an acceptable range. Often, a DTC sets soon after a failed initialization attempt. The message center displays the stability system disabled message when sensor initialization fails.

Dec 082016
 

2007 GMC SierraI keep getting an engine light for my gas cap. It is not a GM part, which costs $35. Is there a sensor for the gas cap that can be disconnected?


RESPONSE

The check engine light comes on when a Diagnostic Trouble Code has been detected. A trouble code for a small evap(evaporative system) leak comes up and the most common reason for this code would be a loose or failed gas cap. If you have just filled the fuel tank I would recommend tightening the cap and driving it a few days to see if it doesn’t cycle back off. The Gas cap can be tested with the proper equipment. Also the evap leak can be located with a smoke machine.

Check Gas Cap Message

 The control module sends a class 2 message to the driver information center (DIC) illuminating the Check Gas Cap message when a malfunction in the evaporative emission (EVAP) system and a large leak test fails.

There is not a sensor that can be disconnected that pertains to the gas cap.

EVAP System Operation

 The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and EVAP vent solenoid valve to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge solenoid valve ON, allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent solenoid valve OFF, fresh air is drawn through the vent solenoid valve and the vent line to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge solenoid valve into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking.

Large Leak Test

 This tests for large leaks and restrictions to the purge path in the evaporative emission (EVAP) system. When the enabling criteria has been met, the control module commands the EVAP vent solenoid valve ON and the EVAP purge solenoid valve ON, allowing vacuum into the EVAP system. The control module monitors the fuel tank pressure (FTP) sensor voltage to verify that the system is able to reach a predetermined level of vacuum within a set amount of time.
Nov 242016
 

GMC SafariI’m trying to figure I have brake lights and directional light no nightlife no night light I change the receptacle with only two wires in the with only two wires in the rain and what am I doing wrong?


RESPONSE

Check the fuses and then the wiring for good ground and current. Then check the switch, wiring harness and connections for no night light.

fuse box diagram 1986 GMC Safari Van - No Night Light

Light operation – No Night Light

The headlight switch is a push button switch to turn the lights on and off. It is is located on the left side of the instrument panel. A rheostat dial, located with the headlight/parking light switch, is used to control the illumination of the instrument panel. It is also used to control the night light.

A dimmer switch (part of the combination switch), to control the Hi and Lo beam operation, is located in the steering column; the lights are changed by pulling the lever toward the driver.

Nov 232016
 

2012-GMC TerrainThe entire display and radio quit working, all fuses are good,? thanks


RESPONSE

The fuses should be Hot at all times. This means you should see battery voltage at each fuse on both sides of the fuse. Double Check these fuses.

Radio Quit – Check These Fuses First

  1. F5DA – 10 amp – located in the instrument panel fuse block(center console)
  2. F31DA – 30 amp – located in the instrument panel fuse block(center console)
  3. F7DA – 5 amp – located in the instrument panel fuse block(center console)
  4. F15DA – 10 amp – located in the instrument panel fuse block(center console)
  5. F19DA – 10 amp – located in the instrument panel fuse block(center console)
  6. F9DA – 20 amp – located in the instrument panel fuse block(center console)
  7. F33DA – 10 amp – located in the instrument panel fuse block(center console)

If all the fuses show good and but you do not see battery voltage at the fuse, trace the wiring going tot he fuse and repair. If you see battery voltage at the fuses on both side, check wiring going to the display and radio. Check the connections. Repair as needed. If wiring and connections check out, it may necessary to replace the radio and or the display.

You may want purchase a full set of wiring diagrams to assist in tracing the circuit.

Nov 202016
 

1998 GMC SonomaCan the lower intake manifold gaskets be replaced without removing the upper intake from the lower? Or can I pull the entire intake as an entire unit?


RESPONSE

Yes. The intake manifold may be removed as an assembly. Do not remove the specific intake manifold components unless component service is required.

intake manifold

Intake Manifold Removal

  • Remove the evaporative emission (EVAP) canister purge solenoid valve harness.
  • Push the quick disconnect clip and hold in place.
  • Pull outward on the harness elbow.
  • Take off the engine coolant temperature (ECT) sensor wire connector (if equipped) from the engine wiring harness bracket.
  • Remove the lower manifold bolts.
  • Remove the manifold assembly.
  • Discard the lower manifold gaskets.

Important The intake manifold may be removed as an assembly. Do not remove the specific  manifold components unless component service is required.
Do not allow dirt or debris to enter the fuel system. Ensure that the ends of the fuel system are properly sealed.
Do not disassemble the Central Sequential Fuel Injection (SFI) unit, unless service is required.

• Inspect the lower intake manifold for the following:

– Cracks or damage

– Damage to the gasket sealing surfaces

– Damage to the threaded bolt holes

– Restricted exhaust gas recirulation (EGR) system passages

– Restricted cooling system passages

Oct 312016
 

1990 GMC SierraI just had a mechanic put in a used rebuilt set of gears in the rear end of my 1991 GMC 1/2 ton 4×4 truck. The problem we are having is when you drive it, it starts out fine then there is a jolt and it acts like it wants to go in revere.
He brought it back to his shop and picked it up and spun the wheels, they seemed fine and then Wham, loud noise and the wheels stop and wanted to go in revere. He is stumped he has never came across this before what could of happened?


RESPONSE

Is the Driveshaft disconnected when spinning the wheels up in the air?

Does the rear end have a Locker Unit? Limited Slip? Or Posi-traction?

Sounds like something has backed off and is periodically catching. Remove Drive Shaft. Drain rear end fluid and remove cover. spin and inspect the work. Make sure the axle clips are not backing out or damaged.

1991 GMC K1500 Rear End Cover

rear end

Sep 282016
 

1999 GMC SafariI Am Unable To Get The Back Hatch Open So The Doors Can’t Open. I Don’t Have Auto Lock & Unlock As It Won’t Work. The Hatch Won’t Open With The Key Either. I Need Info To Remove Inside Door Trim Panel.


RESPONSE

Rear Door Trim Panel Removal with Liftgate

1999-gmc-safari-rear-door-trim-panel-replacement-e54

Rear Door Trim Panel Removal with Liftgate

1999-gmc-safari-rear-door-trim-panel-replacement-cargo-doors
Sep 262016
 

2008 GMC SierraThe air conditioning compressor froze up and can’t afford to fix it right now. How can I drive it without the loud noise or hurt it?


RESPONSE

Remove the Air Conditioning belt.

air conditioning belt diagram 2008 GMC Seirra

 

  • Remove the accessory drive belt.
  • Install a ratchet into the air conditioning (A/C) belt tensioner adapter opening.
  • Rotate the A/C belt tensioner clockwise in order to relieve tension on the A/C belt.
  • Remove the A/C belt from the pulleys.
  • Slowly release the tension on the A/C belt tensioner.
  • Remove the ratchet from the A/C belt tensioner.

 

 

Aug 042016
 

2003 GMC DenaliI had my truck in the shop to get the door fixed. While it was there the battery died due to not being able to shut the door. The mechanic charged it for me and it started fine however when I was in drive or reverse and not giving it gas, it would die. It would restart fine. I also noticed that while in gear and no gas applied the battery gauge would drop. While in neutral or park it idled fine. Today and at a stop sign it died and would not restart. It would turn over but as soon as it caught it died. It started right up with a jump but once the cables where removed it ran for a second or two and died. Took the battery and alternator in and both tested good. What could it be?


RESPONSE

Most likely the battery is bad. And odds are the battery is beyond 4 years old anyway. Once a battery is run completely flat it is difficult to get it live much longer. Also jump starting a battery also causes more damage internally. I recommend replacing the battery first.  And yes, I saw that the test said it was good. I have seen many batteries test good that really are not. Usually if the alternator is faulty, the battery (not charging) light will illuminate on the dash display.