Question: Three months ago, I purchased a 2010 Jeep Wrangler Sport. It came with P255/75R17 tires that are larger than the original tires, which were P225/75R16. Is there an easy and inexpensive fix to recalibrate my speedometer so everything is correct based on the present tire size? Thanks.
F.S.
Answer: Your replacement tires cover about 8.5 per cent more ground per revolution than the stock tires, making both the speedometer and odometer read low by this percentage, regardless of your speed. For example, at an indicated 105 km/h, you鈥檙e actually doing 114 km/h.
Unlike the old days, when one could swap out the speedometer driven gear in the transmission or purchase a gear-driven cable adapter, this will require a software update to the powertrain control module or instrument panel module, as applicable. This could be something for the dealer to take a crack at.
Jeeps and other off-road vehicles are often modified in this and other ways, and there are several aftermarket sources for DIY speedometer/odometer reprogramming. You could either purchase a device such as Rough Country鈥檚 Jeep QuickCal Speedometer Calibrator (applicable to 07-18 Wrangler JK models, about $140 US), or perhaps Hypertech鈥檚 Speedometer Calibrator, which can also serve as an OBD-II code reader, for about $220 US. These plug into the under-dash OBD-II data link connector and make quick work of the task. Another option would be to check with nearby 4X4 specialty shops and see if they can use their tool on your vehicle for possibly a few less bucks.
Q: I was wondering whether the 2001 GMC Sierra HD 2500 Dual Cab truck has ever had an electronic recall. I have an electronic problem that I noticed on at least two other, different GMC trucks I鈥檝e ridden in. Specifically, the ABS/Brake light is almost always on; the gasoline indicator works intermittently; and the radio/clock almost never works. All other gauges work. Internet research brought up a possible problem: electronic cluster. Before I pay for an electronic diagnosis ($150), an electronic cluster (+$500), and installation fee, I wanted to get your input on this. Any ideas?
R.N.
A: I searched and was unable to find a service bulletin, OEM campaign, or recall that would tie any of these faults together, as well as any common physical connection. Certain Chevy and GMC trucks of your vintage were recalled for possible corrosion that might affect the ABS system鈥檚 front wheel speed sensors, resulting in undesired ABS intervention at low vehicle speeds.
I think you may have three different situations. Retrieving diagnostic trouble codes from the ABS system should shed light on the cause of the illuminated warning indicator. When the fuel gauge doesn鈥檛 work, does it go to full or empty? This should help determine a possible cause. A scan tool check of fuel level (info from powertrain control module) versus the instrument gauge would guide a tech to perhaps the fuel tank sending unit as opposed to a possible instrument panel/gauge fault. I鈥檇 start diagnosis of the radio/clock with power and ground checks at the radio鈥檚 connector 1, terminals 5, 9 and 10.
Q: My wife got a nail in her run-flat tire, and they cannot repair those if the nail is in the outer row of tread. Fortunately, we needed only to replace that tire because it had just 11,000 kilometres. And if she gets a flat in the middle of nowhere, she really has a problem because even if you can make it to a garage in the tire鈥檚 80-km range, they will likely not have the tire in stock.
M.R.
A: Yes, run-flat tires are not the panacea that they had hoped. The tires are not cheap, either. Many motorists switch to standard tires when replacement is due. And, nowadays, carmakers are simply providing a kit with tire sealant and a battery-powered compressor in the trunk. It might actually get you home and you might be able to get the tire fixed.
Q: Three days ago, I backed my 2007 Subaru Tribeca down the driveway and applied the brakes. The brake pedal did not depress. After pumping the brakes for about two minutes or more they finally started to work. My wife insisted that she told me this happened every winter when the temperature was below -5 C. I guess I never listened to her. I took the car to the local dealer and he stated this was a typical problem with the 2007 Tribeca and I would waste my money trying to fix the problem. I then checked online and found that this was a common problem that many people had with a freezing check valve going to the booster. This is a serious and dangerous problem and there should be some sort of fix.
J.K.
A: Although uncommon, ice forming in the brake booster鈥檚 vacuum supply hose happens. Usually, it is due to a low point in the hose where water accumulates. Rerouting the hose fixes it. As for Subaru, the problem is different. There is a vacuum check valve in the hose designed to maintain vacuum in the booster for brake application if the engine stalls. First, the source of moisture should be investigated and eliminated, and then the check valve and hose assembly may need to be replaced.
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, California. Readers can email him at [email protected]..
