Looking for Hot Air
Q:The heater in my 1999 ZR2 Blazer quit working. The blower operates but only discharges cool air. Do you have any suggestions?
A:You should analyze the basics before getting the vehicle to a qualified repair shop. First, be sure the radiator and coolant reservoir are full. If your Blazer is equipped with a coolant temperature gauge, observe the reading after running the engine for 15 minutes. The gauge should climb to normal operating temperature. A low gauge reading may indicate that the engine's thermostat is stuck open. This would significantly diminish heater performance. Open the hood and carefully feel the two heater hoses leading through the firewall to the heater core under the dash. The hoses should be hot. Insufficient temperature at the hoses indicates a restriction in coolant delivery from the engine. Hot hoses would steer you toward a temperature-control problem within the system under the dash. There have been problems with coolant-system rust buildup on certain GM SUVs that may hamper coolant flow and cause an overheat and/or heater performance problem. In this case, GM TSB #99-06-02-012D gives a detailed coolant-system inspection and flushing procedure.
Airbag Replacement Tips
Q:My 1996 GMC Sierra deployed an airbag, and I can't get a straight answer as to what parts I need to replace. A low-speed collision triggered the deployment, and the frame-rail sensor wasn't damaged. I've been told there's a sensor under the seat that has to be replaced, but I can't find it. Is there a way to ohm the frame-rail sensor to check? Will the new bag deploy if I've overlooked something and reconnect the power? Can the computer diagnose what I need to replace? I've already purchased some of the parts, which came from a rollover I located at a salvage yard. The local dealership wants a fortune for everything new.
A:There are three sensors: an arming sensor inside the left frame rail below the driver's door and two discriminating sensors outside the left and right front frame rails. These sensors measure sudden changes in vehicle speed and direct airbag deployment. Once an airbag is deployed, the recommended procedure is to repair all structural damage and replace the airbag and any sensors in the area of the damage, even if they appear to be in working condition. Always disconnect the battery and wait two minutes for the system to discharge to avoid accidental deployment during service. There is no sensor under the seat--the module controlling the system is under the dash. Any mounting brackets that were bent in the collision also should be replaced. Next, do a full inspection of the steering column and supplemental inflatable restraint system wiring within the column. The proper scan tool is needed to clear trouble codes from the memory and turn off the airbag warning light. It should go without saying that it's always best to have a trained professional perform this type of work. Not surprisingly, General Motors strongly advises against the use of SIR system parts from another vehicle. There may be hidden internal differences or damage.