Top 20 1999 GMC Sierra Questions & Answers

Why are you needing the VATS module? If you are trying to bypass the VAST system, you only need the two wires at the base of the column that run to the ignition exciter ring.

There may be a short in the front socket. Remove the bulb and inspect the socket for damage. If corroded, clean it up or replace it.

Not true that GM dealer is the only one that can fix it . There are other independent repair shops that can, Transmission repair shops like AAMCO . You could too if you had access to a scan tool that can read DTC'S - diagnostic trouble codes for the 4X4 system . There is a 4X4 control module that can store DTC'S when problems happen . When a warning like check 4 Wheel Drive light's up ,it's not meant for you to do anything except take it to the dealer ,well ,that's what the dealer would like . Would need to know which 4X4 transfer case your's has ? Two speed manual , two speed selectable , two speed automatic ? Their are a few different one's Transfer Case - BW 4401 (Two Speed Manual) Transfer Case - BW 4470 (Two Speed Manual) Transfer Case - NVG 241-NP2 (Two Speed Manual) Transfer Case - NVG 243-NP1 (Two Speed Selectable) Transfer Case - NVG 246-NP8 (Two Speed Automatic) Two speed Automatic system can set a number of codes DTC B0768 Service Indicator Circuit High DTC B2725 ATC Mode Switch Circuit Malfunction DTC C0300 Rear Speed Sensor Malfunction DTC C0305 Front Speed Sensor Malfunction DTC C0308 Motor A/B Circuit Low DTC C0309 Motor A/B Circuit High DTC C0310 Motor A/B Circuit Open DTC C0315 Motor Ground Circuit Open DTC C0323 T-Case Lock Circuit Low DTC C0324 T-Case Lock Circuit High DTC C0327 Encoder Circuit Malfunction DTC C0357 Park Switch Circuit High DTC C0362 4LO Discrete Output Circuit High DTC C0367 Front Axle Control Circuit High DTC C0374 General System Malfunction DTC C0376 Front/Rear Shaft Speed Mismatch DTC C0387 Unable to Perform Shift DTC C0550 ECU Malfunction DTC C0611 VIN Information Error Without having this info you could go round an round an never find the problem .

Check u-joints on drive shaft.

Sometimes heat and vibration can cause filters to loosen enough to leak if not tightened enough when initially installed .

check unversal on drive shaft. put in neutral and shake drive shaft

only one way to solve the the problem is company service and repair manual which will guide with diagram step by step to fix the problem and you can get the manual from the given link http://toolsnyou.com/

I had a 91 GMC 4.3 do the same thing. Liked to froze to ***** one winter. Found I had a air bubble (air lock) in the engine block and heater. It was a bear to get out. Finally installed back flush kit in the heater hose between engine and heater. Took cap off flush kit, pour coolant in through outlet till coolant ran through back to radiator. Replaced cap and started engine. Repeated again. Heater works as good as new. It's using the same principle as priming a gas powered water pump.

It actually sounds like you have a cold or cracked solder joint or you have oxidation on your connector or socket to the display module. Unplug then plug in your display module several times to attempt to remove the oxidation and see if that helps.

What engine ? 4.3 , 4.8 , 5.3 or 6.0 l What fuel injection system ? What is the fuel pressure ? Do you know what fuel trims are ? The fuel pressure regulator's are prone to leaking to leaking on thses SPI injection system./ How to identify and repair leaking fuel pressure regulator GM CPI system...

knock sensor problems arise from ---wiring --poor connections --knock sensor----insecure KS--KS incorrectly tightened ---wiring short to positive --wiring short to ground ---ECM as you can see , there are more causes than the KS itself so care should be taken in the installation, tightening , wires and make sure that the area is water proof

Change the coolant sending unit for the gauge. Usually this is different than the Coolant Temp. Sensor which is for the pcm. Maybe the sending unit is no longer functioning correctly after overheating. Of course, a scanner could show the temperature as recorded by the CTS, or you could use a hand held infrared temperature device to get a better idea of the true temperature.

Check/change transfer case fluid and check the wire connection to it.

If I understand right, I would say the normal ground for the pump is bad. "I am guessing the pump uses a ground source to start." well, just the normal ground like for any motor, you have the power wire (gray) to the pump, then the ground wire for pump, does it branch off near the tank and find a ground? Or does it go into the tank connector and then routed back somewhere through the wiring harness? Anyway, it has to go to ground somewhere. You have the wiring right it sounds,. just make a good ground source, or find the original ground and repair it.

What size engine ? As this vehicle could have come with four different one's. 5.0 , 5.7 , 6.5 and a 7.4 L

You can go to an auto parts store and purchase a manual for your vehicle.

The Internet, though, has a large number of web sites where you can buy service manuals and schematics from bookstores, publishers, and other collectors. Here is just a sampling of what sites are out there: Factory Auto manuals http://www.factoryautomanuals.com/ search for : factory service auto repair manuals Repair Service Manuals http://www.repairservicemanuals.com/ the largest collection of Automotive Repair Service Manuals and Owners Guides on the internet. Our database currently holds over 54,000 entries dating back from 1940 to more recent 2011. about Chilton Repair Manuals http://www.chilton.cengage.com/ about Haynes Repair Manuals Haynes Publishing Haynes auto manuals http://www.haynes.com/

171 code bank one lean 174 bank two lean
possible vaccum leak

The speed sensor is on the output shaft of the transmission. Either it was damaged or not hooked back up.

the power to what switch?, Ignition?, window switch?, sunroof switch?. Please be more specific with your details. This will help us to give you more professional advice.