Electrical or transmission problems with Hummer

ANSWER : Hi there. This vehicle is known for having a history of electrical issues. From the symptoms you are getting it sounds like a bad ignition switch or a failing body control module. Most of the time it is the ignition switch. When it fails internally it causes these systems to act up almost like the key is being turned off and on. This can be diagnosed with a voltage meter by doing a voltage drop test on the switch. If the switch is fine then the body control module will need to be replaced. If this is something that you want to have diagnosed, consider YourMechanic, as a certified mechanic can come to your office to inspect your electrical problems.

ANSWER : Hi There,
This may be an issue related to the communication of the PCM and the TCM (Transmission control module). As you may know, the TCM relies on the PCM to transmit information related to RPM’s, which the TCM then uses to determine when to direct the transmission to shift. The transmission control module has various sensors such as vehicle speed sensors, wheel speed sensors, throttle position sensors, turbine speed sensor, and transmission fluid temperature sensors that all direct information to it in order for it to perform it’s function. Other functions controlled by the TCM are components such as a kick down switch, traction control system, and cruise control module. Any of these may also affect the way the transmission control module performs and controls the transmission and the shifting of your vehicle. I would suggest having a professional from Your Mechanic come to your location to properly diagnose your transmission problem.

ANSWER : The transmission on your car has electronic controls and shift solenoids which control gear changes. I suggest getting a thorough test on your transmission to determine possible causes of the failure before overhauling the transmission. The computer should be scanned for codes and all wiring should be checked. Check the transmission fluid for signs of being burned or contaminated. The transmission cooler and lines should also be flushed out. Since your car is not drivable, contact YourMechanic to check the transmission and get a diagnosis so you do not replace the transmission if only a solenoid in the transmission is bad.

ANSWER : Hi Jose: Thanks for your question. Below is some additional information in addition to that sent to you by John yesterday. Installing used parts, particularly a part as complex as a transmission, is not the best practice. If you have a transmission fault, the first thing to do is get the cause of the fault professionally diagnosed because some transmission faults are easy to fix, such as low fluid level, replacement of burnt fluid, or needed fixes on engine controls or wiring (transmissions are electronically controlled). YourMechanic offers that service as a transmission diagnostic and you can schedule that at your convenience.

After you know, for sure, what is wrong with the transmission then a decision can be made as to the most economic and effective repair strategy. That is, if the fix is not amongst the simple causes of transmission breakdowns, but rather is due to something like a worn out band, or a leaking clutch piston, then the transmission has to be removed, completely overhauled and re-installed, usually with a new torque converter. Without a diagnostic, even installing a new transmission may not resolve your issue if the fault lies in an engine control or electronic control component and this is why you need to first get the problem identified. Hope we can assist you with this.

ANSWER : Hi, thanks for writing in. The cruise control uses some of the same sensor inputs the transmission uses and can indeed affect the transmission and cruise control. If the transmission is slipping then the cruise control may not control the speed steady. Have the transmission problem diagnosed and fixed then see if cruise control problems go away.

ANSWER : It is possible that this is a transmission control module issue. As you may already know the transmission control module provides direction to the transmission as to shifting points, clutching and a wide variety of other control related transmission functions. Check to be sure there is a proper amount of transmission fluid in it. I would suspect that based upon your descriptions there is most likely a Check Engine Light on in your dash. This will register a fault code in the car’s computer which will provide detail as to the specific problems the transmission may be having. You will need a specific type of scanning tool that works directly with the transmission ECM rather than your car’s main computer. I would recommend having an expert from YourMechanic come to your home to diagnose your possible faulty transmission and make repairs.

ANSWER : Hi there. Why was the alternator replaced? Was the battery tested with a digital tester that provides current voltage, cold cranking amps, and state of health? If not, I suggest having that battery tested. A bad cell inside the battery can wreak havoc on electrically controlled systems; especially computer controlled systems. This cell can create voltage spikes and dips where there should be none. I suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several available technicians that can assist you with an electrical problems inspection.

ANSWER : Hi there. You will need to first find the coolant leak and address the leak and get it fixed. The engine may overheat and cause even more problems. The transmission or engine misfires could be from the coolant leak if the coolant is getting onto the wiring of the engine. You may also be going into failure mode if the engine is running hot. Have the cooling system diagnosed and repaired first and any coolant leaks on the harnesses cleaned of coolant that may have got in connections. Then scan and test systems for further problems and diagnosis needed.