Drastic Drop in Mileage Points Finger at Part Replacement

November 20, 2010/Steve Tackett


Dear Doctor: Due to some electric malfunctions, a local shop changed the power module in my beloved 2002 Pontiac Aztek. Friends make fun of the car’s ugliness, but I happen to like it a lot, particularly because of the excellent fuel mileage, which was consistently in the low 20s during the first 50,000 miles. But after replacement of the power module, the mileage has now dropped off into the teens. The repair shop says it can’t be due to the module, but there’s been no other work done. What could it be? Bob
Dear Bob: Anytime there is a drastic drop in fuel economy after an electronic part is replaced, we need to step back and check the replacement electronic part and make sure it is the correct part and has been updated (flashed), if applicable. Take it to the shop and have the technician hook up a professional scan tool for a road test. Drive the car while the technician monitors all the computer information, including the oxygen sensor, engine temperature and make sure the transmission is shifting into overdrive.
Dear Doctor: On cool mornings, the steering wheel on my 1998 Volkswagen Passat is very hard to turn. When I make left turns the wheel is sluggish, then I’ll hear a ping from the engine compartment, and the wheel starts to turn easily. This does not happen with right turns. I put the front-end on blocks and turned the wheel back and forth between the stops for about 30 seconds. There was no resistance or pinging sounds in either case. Can you offer suggestions? Wes
Dear Wes: If the steering wheel binds turning to the left only and there is a noise emitting and then the steering is normal, then something is binding up. It could be many things, including a faulty power steering rack, front-end chassis part, even a stiff outer C/V axle joint. It is hard to check the car without weight on the front-end parts. A drive-on style lift will be needed or the technician will disconnect chassis parts and see if there is any binding.
Dear Doctor: The airbag gauge light illuminated on my 2004 Hyundai, so the mechanic cleared it. He said his computer software indicated the problem is under the passenger seat. Two months later the light is back on so I took a look and found a half dozen wires. Is this the main airbag unit or is it under the other seats, too? What is the function of all the wires and the unit? I bought a code diagnostic tool thinking I would get answers. No way — no airbag information. Charles
Dear Charles: There are items on a car that need the service of a professional and the airbag circuit is one of them.

2006 Cadillac CTS

You mentioned you purchased a scan tool. The professional computer version used by qualified technicians costs $7,000, plus $1,000 for the annual upgrade. As for the airbag module under the seat, I recommend you go to the dealership. Some airbag components do have an extended warranty. The problem could be a minor a seat belt issue.
Dear Doctor: I have a 1996 Ford Mustang 4.6-liter V-8 with the “check engine” light. Diagnostic test fault codes read evaporation system, shorted purge flow sensor, plus codes 171 and 174 (right and left cylinder banks running lean). I replaced the defective parts and cleared the fault codes. The car ran great for 60 miles, but the “check engine” light came back on. The same fault codes showed. The Mustang also has an aftermarket cold air intake system. Any advice? Bill
Dear Bill: The fault codes 171 and 174 are indeed lean codes. You need to find out when the codes were set what the readings were on the engine temperature and the engine speed. The use of a high-performance air filter can add to a lean condition, especially on late model vehicles. Intake vacuum leaks, or any vacuum leak, dirty mass air flow meters are all common culprits on Ford vehicles.
Dear Doctor: I own a 2006 Cadillac CTS-V with the six-speed manual transmission with a few modifications. I’m wondering whether to remove the engine and build it with a supercharger or buy a new 2011. Have you driven a new CTS-V and what do you suggest? Mark
Dear Mark: My answer is this: if you can afford to buy a 2009 or newer the difference is night and day from your 2006 model. In fact I did drive the new 2011 CTS-V coupe with the six-speed automatic. The CTS-V is an all-new car — suspension included. At 556 horsepower mated to either a six-speed manual or automatic, the CTS-V is the most bang for the buck in a luxury performance car. One option that is a driver’s choice is the Recaro seats. Make sure you are comfortable in them. With a few bolt-on power options the engine will produce over 600 friendly smooth horsepower. — Junior Damato, Motor Matters

Junior Damato is an ASE-certified Master Technician.

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Copyright, Motor Matters, 2010