Auto Doctor: Changes to intake, exhaust systems require reprogramming

When vehicles with keyless ignition and dealer-installed remote

When vehicles with keyless ignition and dealer-installed remote start, such as the 2009 Nissan Altima, start acting up, the auto doctor recommends removing the remote starter system completely to diagnose the problem. (Credit: Nissan)

Dear Doctor: My 2009 Nissan Altima with keyless ignition and dealer-installed remote start has only 18,000 miles and has been acting erratically lately. On two occasions the vehicle would not start, but eventually did after 5 minutes. I also experienced an incident where the car horn was blaring while parked in my driveway. One day I noticed the dashboard and interior lights on and the vehicle cranking on its own -- and key fob was not on me. I have changed both fob batteries three times in the past three months; they keep on draining. My Nissan dealer has been unable to diagnose this. Any advice? -- Johnny

Dear Johnny: Any time we get a vehicle with this condition involving a remote starter, we disconnect the remote starter system completely, and then see if there are any changes before starting any diagnoses. There has to be something in the electronic system that causes the problems you are having and it could be remote starter related. If the problem still exists we would then check all Technical Service Bulletins and contact our partners at Identifix technical support.

Dear Doctor: I have a 2000 GMC 2500 4WD extended cab pickup that goes into a vibration mode intermittently at 35 to 60 mph. I pulled the drive shaft out and found everything to be OK. The cab mounts, front end joints and wheel bearings are all fine. Still, the truck feels like those "wake-up strips" on the highway, but it goes away when I let up on the gas. I don't feel it much in the steering wheel -- seems more like in the drivetrain. Any advice? -- Daniel


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Dear Daniel: From you description there is no question that there is a driveline problem. You need to start with shifting down a gear in the transmission and see if the problem still persists. The on/off the gas pedal reaction you are getting indicates a possible transmission and/or universal joint problem. You also need to check the transfer case to front-drive differential universal joints, as well as check whether the front-drive shaft is engaged, even if the 4x4 switch is in 2WD.

Dear Doctor: I own a 2008 Dodge Charger R/T 5.7 Hemi (MDS) with currently 29,200 on the odometer. According to the owner's manual, spark plugs (all 16) need to be changed at 30,000 miles or 30 months. I did change the plugs at 32 months and it's time to change them again. Are there plugs that will last longer before requiring to be changed or is this an issue relating to the aluminum heads? Will not changing the plugs in this time frame invalidate the lifetime power-train warranty? In addition what are your thoughts on installing a lower temperature thermostat? -- George

Dear George: Spark plug replacement is critical on a lot of vehicles. Your Hemi engine requires spark plug replacement for two main reasons: for engine performance and low emissions. Also, to prevent spark plugs from getting stuck in the cylinder head. There are no magical spark plugs that will extend replacement intervals.

Dear Doctor: I have a 2011 Chevy Silverado with the 5.3 motor. I have installed a spectrum cold air intake. Since the installation the "check engine" light has been going on and off. I read the code and it says lean bank 1 and 2. The truck will not pass inspection, so I put the original air box back on, cleared code, and did drive cycle. All was fine and passed inspection. What do you think is the cause of the problem? -- Tom

Dear Tom: Great question and you are not alone with this type of problem. Today's vehicles are designed to run as lean as possible with the factory air intake and exhaust systems. Some vehicles will not even idle with the addition of a fresh air intake without a computer reprogramming. There are many companies that offer reprogrammers. They all work the same way; some offer more features that others. The power increase is very noticeable, as well as transmission firmness and shift points.

Dear Doctor: I have a 2006 Nissan Xterra 4x4 with 86,000 miles and I just replaced the radiator as I did not want water and transmission fluid to mix. All went well, but as I looked into the throttle body I saw it was very dirty. I took a rag and put gum-out on it and cleaned it. When done I put everything back. Now the "check engine" light is illuminating with code PO507 and the engine stays revved in drive. What do advise I do next? -- Peter

Dear Peter: First, to all my readers: Never clean an electronic throttle body in any car or truck. You will do more damage than good. The high idle and fault code p0507 indicate the throttle body needs to be relearned. Per our Identifix support we're informed of Technical Service Bulletin NTB05-067, referring to gas pedal release position learning procedure. You can bring the vehicle to a qualified ASE technician. Under some circumstances a factory scan tool may be required to relearn the system.  -- Junior Damato, Motor Matters

Junior Damato is an ASE-certified Master Technician. Email questions to info@motormatters.biz. Mail questions to: Auto Doctor, 3 Court Circle, Lakeville, MA 02347

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