Why the false mileage readings on the odometer?

Dear Doctor: My friend owns a 2017 Dodge Grand Caravan with 5,000 miles. She has seen the odometer “jump” by 100 miles (2,999 odometer miles turning to 3,100 instead of 3,000 miles). Her minivan was driven from Georgia to New York, along with a motorist in a second car — with both drivers taking the exact same route, but their mileage readings differed by 300 miles! Why?

— Carl

Dear Carl: Today’s vehicle speedometers and odometers are electronically controlled. They receive signals to the computer via a speed sensor. Any electronic interference or voltage spike can cause a stray signal, and yes, cause the odometer to skip a beat and/or alter mileage. The signal is called EMI (electronic magnetic interference). There are multiple electronic signals in the airwaves and some can cause all kinds of issues. However, vehicles do have many filters and filtering devices to help prevent false input signals as much as possible.

Dear Doctor: Four days after replacing the battery on my 2015 Honda Accord V-6 with a manual transmission and push-button start, the “starter system” light came on. Prior, there was a delay in the engine turning over after the clutch was depressed and the starter button pushed. The first time this happened my dealer cleared the codes, which they acknowledged hadn’t been done when the new battery was installed. The car was OK for two days, but the same thing happened again. Then the dealer replaced the clutch sensor, which wasn’t working. What’s your opinion on this?

— Joann

Dear Joann: The battery replacement would not be connected with the push-to-start system. The starter system starts at the switch, then to the clutch pedal safety switch, then to a solenoid, and finally to the (S) terminal on the starter motor. Have a technician connect a test light to the (S) terminal at the starter. Push the start button and depress the clutch, and check to see whether power is at the starter. If there is no power, then the technician would check power at the clutch safety position sensor.

Dear Doctor: My 2005 Hyundai Tucson has 52,000 miles. I drove a short distance and it started to cut out. I pulled over, it was still running, and I revved the engine and started moving again but it went 10 feet, then stopped running and would not start. It was taken to a repair center on a flatbed. The next day they started it right up and it ran fine. They checked the computer and found codes PO301 and PO304. They did a 30-minute road test and idled it for another 30 minutes. It started up every time and didn’t cut out. But they told me it could happen again soon, or not for a long time. It’s unnerving not knowing. What would you do?

— Ed

Dear Ed: These fault codes indicate a misfire on cylinders 1 and 4. Your vehicle is 10-plus years old with with very low mileage. If you’ve never changed the spark plugs, then I recommend a replacement as a good place to start to resolve the issue. The misfire you experienced is more ignition-related, than mechanical. Your mechanic should have looked in freeze-frame mode to see exactly when the misfire occurred, at what engine speed, accelerator position, engine load, plus more. Find a technician who utilizes both Alldata and Identifix services, both of which would offer professional assistance in getting to the bottom of this issue.

E-mail questions for publication to info@motormatters.biz. Mail questions with SASE to: Motor Matters, PO Box 3305, Wilmington, DE 19804


Today's breaking news and more in your inbox

I'm interested in (please check all that apply)