Automobile / GMC / 1500 Truck

GMC 1500 Truck Repair Questions and Answers

Question: 1997 GMC 1500 4WD mileage: 98,000. Idles good for about 5 minutes. Starts idling rough once engine warms. I have so far replaced the following items and performed following repairs: 1. New cap/rotor, plugs, wires, coil and distributor. 2. New EGR valve. 3. Mass air flow sensor. 4. New fuel filter. 5. Cleaned all electrical grounds and battery posts. Idles like it's missing. Doesn't stall but is rough. The IAC valve checks good and pintle is clean. Timed engine and noticed power improvement as well as mpg. Baffled as to why it idles rough only when warm?

Answer: Try replacing coolant temperature sensor you would not believe the problems you get when a simple sensor fails.

Follow-up: I would have never guessed this in a million years. The truck has been running very cool lately, never getting over 160 deg F. Upon reading the service manual, there is only one short sentence that GM decided to make note of (and it wasn't listed as a remedy to my problem). The coolant temp sensor is a key sensor on this truck. The computer sends a 5-volt signal to the sensor and dependent upon the resistance of the sensor (coolant temperature), a lower volt signal is returned to the computer. The computer sees this voltage and commands the other sensors, one of which is the IAC Idle Air Control Valve to adjust idle speed accordingly. Since the coolant sensor is new, I came to the conclusion that my THERMOSTAT WAS STUCK OPEN! This explains the temperature never reaching above 160 deg F. This thermostat operates normally at a range of 188-206 deg F. So, once the truck warmed up and I started having rough idle problems, the coolant temperature sensor was never sending a proper return voltage signal to the computer for it to command proper operation of the rest of the sensors. This coolant temp sensor is the KEY sensor on engine performance! The computer was fooled in believing the truck never reached full warm up to instruct the IAC with a proper calibration signal. The poor IAC was "searching" for an optimal setting the whole time, causing my poor idle and roughness. This whole episode explains why you see cars and trucks in colder climates with owners who purposely cut cardboard or other materials to partially block airflow to the radiator to maintain temperature for proper thermostat operation thus proper engine performance.

Question: 2002 GMC 1500 pickup mileage: 58,000. Has anyone been asking questions about steering problems on these trucks? My steering wheel suddenly "frees up" and turns easier when I go around a right turn. It almost feels like the steering wheel is being jerked out of your hand. I called 3 different GMC dealers and got 3 different answers. I was told it could be the power steering pump, the power steering gearbox, or the sensor on the steering column. I was told by 2 of the dealers that there is a problem, but it has not been recalled.

Answer: We think that you may have a bad steering column sensor.

Question:  1989 GMC Z-71 350  mileage: 25,000.   My truck started making a strange noise the other day whenever I would accelerate.  It makes a whining or squealing sound, but only when I accelerate not when I let of the gas or coast.  I checked the transmission fluid, but I am not sure what else it might be.  I could use your help!

Answer:   We think that your squealing sound may be caused by a loose or worn out fan belt.

Question:  1998 GMC Pickup Full Size Bed mileage: 80,000.  When accelerating, the automatic transmission will not shift into the next higher gear unless I take my foot off the gas a bit.  In addition, the engine must be racing before I can let off the gas to get it to shift up.  Downshifts fine.   What do you think is causing the problem?   Thanks in advance.

Answer:   Check the vacuum modulator.  It may need replacing.  Also, check the vacuum hose to the modulator for leaks or lose connections.

Question:  1999 GMC 2500 mileage: 103,000.  Is it possible to disassemble the turn signal lever to get at the cruise control switches?   I had to do some repair of the tilt steering wheel mechanism, and in the process, I must have disrupted the cruise control circuitry as the cruise no longer works.  I have checked for electrical continuity back through the switches by checking at the 4-wire connector under the dashboard and have none.  I am hoping that it is possible to disassemble the so-called multi-function lever so that I can see what the problem is.  (All other functions that are on the turn signal lever are operational)  Thanks for your help!

Answer:    Sorry, the turn signal assembly must be replaced.  It is not a serviceable part.

Question:  1998 GMC 2500  mileage: 135,000.  While driving my GMC pick-up I noticed the service engine light kept going on and off.   I also noticed that now when I stopped at a light or put the truck in park, I have a very high idle.  The truck runs fine except for the fast idle.  I didn't really have time to take it to a mechanic and kept putting it off because I have a company car for work so only use the truck after work or weekends.   Well, after about 3 weeks (I know I should have taken it to a repair shop) the light went off and the idle back to normal.  Then it was o k for about a month.  Now the idle is high again but the service engine light does not come on.   I was told how to extract the trouble codes from the ECM and got the codes 22, 33, 34.  I replaced the TPS, and the MAP sensor, reset the ECM.  Well, the engine still has a high idle; yet, there are no trouble codes.  The vacuum lines all appear to be OK.  I'm lost.........the truck runs great except for the high idle, which seems to have just came from nowhere.  PS....The throttle linkage is free and clear, and the EGR valve seems OK,.........PLEASE HELP!!!!!!!!!!

Answer:   Check the throttle body gasket.  It may have failed.

Question: I have a 1995 GMC Truck. The wire harness for the tail lights was taken off and put back on, and now they don't work. One blinker works ok and the other is very dim. There are no running lights or brake lights.  Any suggestions?

Answer: Sounds like you have a poor ground connection between the tail light assembly and the fender. Clean the mounting surfaces or add an extra ground wire from the tail-light housing to the frame

Automobile / GMC / 1500 Truck

Look up more 1500 Truck Questions in our Car Repair forum section.

Try looking up your problem in our Auto Repair topics section.

Got a 1500 Truck Repair Question? We will answer it for free.

Replace Air Filter

Check Engine Light