​According to a 2016 survey of 1,000 drivers conducted by the Rubber Manufacturers Association, the average consumer doesn't have adequate knowledge about proper tire inflation maintenance. 

• Only 17% of drivers are "tire smart," or know how to properly check tire pressure. 
• Only 50% of drivers know where to find the correct inflation pressure for their vehicle: The label on a vehicle's driver-side door or owner's manual. Fifty percent of drivers wrongly believe that the correct pressure is listed on the tire sidewall. 
• One out of three drivers don't know that tires should be checked "cold" before driving. One of the biggest mistakes you can make is checking tires after driving. As tires roll, they warm up, which causes the pressure to increase. This could yield a false tire pressure reading. 
• Four in 10 drivers believe they can tell if a tire is under-inflated just by looking. 
• Two out of three drivers do not check the tire pressure in their spare tire. 

Having your tires inflated to the correct pressure is critical for alignments, TPMS (Tire Pressure Monitor System) service, and maintaining fuel efficiency. If you are not filling your tires to their correct tire pressure, you could be setting yourself up for failure, so never underestimate the value of proper tire inflation.

Nearly every vehicle owner's manual and door jamb placard recommends tire pressure be set when the tires are cold, but what is 'cold'? As a general recommendation, most OEMs say that the tire should be sitting for at least three hours. 

Ambient temperature affects tire pressure on every tire. For every increase or decrease of 10°F of ambient temperature, tire pressures will change about 2%, or about 1 psi (pounds per square inch) for the average passenger vehicle tire. 

If a tire's pressure was set on a summer day when it is 90° F and it is now 40° F, the tire will have lost 4-5 psi just due to changes in temperature. On some vehicles, this could cause the TPMS light to illuminate. It also works the other way around. If a tire was inflated at 40° F and the outside temperature is now 90° F, the tire could now be over-inflated. 

Always take outside and indoor temperature into consideration when setting inflation. For example, a 40° F discrepancy may require you to add 3 to 4 psi (40° F = 4 psi) over the placard pressure to account for cooling when the vehicle has been parked outside. If this is done correctly, the cool pressure should be close to the specified cold pressure. As a general rule, never set the tire pressure below the specified placard value regardless of tire temperature or ambient temperature. Some late-model vehicles can take the ambient air temperature into account to avoid false activation of the TPMS light.

Before you top off a tire, take some time to investigate where the air has gone. On late-model vehicles with TPMS, one of the leading causes of slow leaks can be a neglected service kit for the TPMS sensors. Some service providers can assume they are doing their customer a favor by saving them the expense of installing a new service kit, but that is not the case. 

Often the sensor will be hit during removal or installation and the seal between the rim and the sensor's valve stem will be disturbed. This can cause a slow leak. In addition, the service parts of the sensor have a limited lifespan because the heat from the brakes and other environmental contaminants can cause the soft components to degrade and the metal components to corrode.

With that said, never reuse nuts, grommets or valve stems. Aluminum TPMS valve stems and nuts are anodized to prevent galvanic corrosion and material deterioration. The nut has a bonded lubricant to help provide the proper torque required for seating a new grommet. If a nut is reused, the anodized surface may be scratched away and corrosion may occur between the sensor, wheel, and stem. 

Snap-in valve stems and grommets conform to the mating surface of the rim. The instant the nut is torqued or a valve stem is pulled through the rim, it starts to take on the shape of the surfaces against which it is sealing. This memory cannot be erased, so if the seal is reused, it could cause a slow leak. 

Setting the correct tire inflation should be one of the first steps of performing an alignment. Not setting the correct tire pressure could cause a misaligned vehicle that pulls no matter how perfect the toe and thrust angles are set. 

If the rear tire pressures are too low or high, they can change the caster setting. This could cause poor steering feel and hurt straight-line stability. If the front tires don't have the same pressures, they could cause the vehicle to pull in the direction of the lowest tire.

Buy a quality tire pressure gauge. We advise our customers to purchase a digital gauge to check their tires in between services. A quality tire pressure gauge should have a tolerance of plus or minus 1%. Anything beyond 2% can cause you to set tire pressures too low or too high. Also, treat your tire gauge like it's your new iPhone. No, your screen may not shatter, but dropping a tire gauge from only 4 feet can change the readings -- this goes for both digital and analog gauges.

by Mike Souza (ATRA Memeber)
Gears Magazine December 2011

Once upon a time, when a car came in with a transmission problem, there was a really good chance there was something wrong with the transmission. Batteries? Tires? Tailgates? Those were someone else's problems... they certainly had nothing to do with the transmission operation. 

These days? Well, weird things happen every day. Like transmission problems caused by low voltage, poor cable connections, or loose or dirty grounds. And to make things even weirder, the battery may still start the engine without being jumped or the terminals cleaned. 

So how do you deal with transmission problems caused by the battery? Start by cleaning and tightening the battery terminal ends before chasing electrical codes. Even if the terminals look good and the vehicle starts without a problem. And if it looks like this one (Right, below for mobile readers) don't even think of going any further until you clean the terminals and check the voltage. This particular instance was a 41TE where a shop worked on it for two days for solenoid codes.        

Here are five examples of cars with battery problems that affected transmission operation:

1. A Saturn equipped with a TAAT transmission had a complaint of hard shifts. There were no codes stored in any module. The battery voltage was low, but the engine started without any problems Charging the battery corrected the hard shifts. 
2. 2004 Saturn Vue with the MDRA Honda-type 5-speed transmission had a slip or delay on forward engagement. It sometimes fell out of gear at stop or defaulted to second-gear starts. The wrench light on the dash would light sometimes, but there were no codes present. Checking the battery revealed it would develop only 11.9 volts; replacing the battery fixed the transmission problem.
3. Dodge or Chrysler vehicles cycle in and out of lockup or 4th gear without any codes stored. This symptom appears most often at light throttle, between 35 to 45 miles per hour. There's a list of 22 or more issues that can cause this complaint, but the most common is loos or dirty battery terminals and poor ground connections. 
4. Ford trucks equipped with a power takeoff (PTO) unit ; the PTO stops working after a transmission rebuild. There's no problem with the battery voltage or connections; the problem was cause when the battery was disconnected during repair, causing the computer to lose its memories. TO correct it, you'll need to drive the vehicle for at least 7 miles at speeds over 50 MPH for the computer to relearn PTO function. 
5. Late model Mercedes vehicles with a weak battery or a replacement battery that won't provide adequate current for the starter. This can cause pump bushing failure because of the additional starter draw through the transmission bell housing. 

And the weirdness doesn't end with the battery: Weird things can happen to the transmission because of tire problems, too. Problems such as low pressure, wrong size, or mismatched brands can cause a range of "transmission" problems. 


For example: A BMW equipped with either a 4L30E, or ZF 4- or 5-Speed transmission won't upshift to or past 4th gear after driving on the highway. The transmission receives commands to only 3rd or 4th gear, with no codes stored. 
This particular vehicle had only 42,000 miles, and the right front tire was just changed because it went flat. The spare was new and had no mileage on it. The difference in tire size caused the computer to think the vehicle was in a high speed turn. The curve recognition software would downshift the vehicle to a lower gear and wouldn't allow the transmission to upshift past that gear. This is a safety feature to prevent the driver from losing control of the vehicle on high speed turns. The quick check for this problem was to swap the tire from the right front to the right rear. 
There' a list a mile long of all the issues tires can cause on 4-wheel drive vehicles. The most common complaints are clunks noises, and binding on turns, to name just a few. Use a stagger gauge to check each tire's size when working on these vehicles. An alternate check would be to mark each tire at the bottom with chalk, then roll the car straight until each tire makes 10 revolutions. All 4 tire marks must be within 1/4" of one another. This method might not yet yield accurate results, as even a slight variation in wheel direction can affect the tire position.

Another quick test: If you have a sand or dirt road nearby, drive off the pavement and onto the sand or dirt road. if you notice a sudden jump in rotation, you're probably dealing with a tire size or pressure problem.

Probably some of the weirdest conditions can be caused by problems with the vehicle's lights. And these conditions can be the most difficult to diagnose.

For example: Some early model Ford trucks may develop harsh shifts; at the same time, the odometer stops working. These vehicles are quipped with a programmable speedodometer/odometer module (PSOM) located inside the instrument cluster. No need to connect the scan tool to this vehicle: just look up at the dome light If it isn't working , the fuse for the PSOM may be blown. A short in the interior lights can cause a circuit problem.

Another problem with Ford trucks can occur with the taillights If someone replaced the original, incandescent, factory-style bulbs with light emitting diode (LED) bulbs, the PCM will think the brakes are being applied. The torque converter will cycle in and out at 25 to 30 percent throttle opening. The same conditions will occur if the cab-mounted brake light is blown, or changed to an LED bulb.  


Hyundai vehicles equipped with an F4A40 or 50-series transmission may stop moving forward when the backup lights are on. A Short in the taillight circuit can back feed into the reverse light range sensor circuit. The TCM is programmed to failsafe to neutral when a signal of reverse and drive occur at the same time. On this vehicle there were no codes stored in any module, and the problem wasn't identified until the transmission was replaced with another unit.

So you have these weird transmission problems that people spend days on, only to find that they're something simple... and completely unrelated to the transmission. Knowing this, maybe you'll remember to check more than just the fluid level.

Here's a set of basic checks that should help you isolate some of the weird problems:

• Fluid level
• Battery voltage (12.4V minimum)
• Battery ground
• Battery cables and terminal ends
• Body grounds
• Interior light function
• Exterior light function
• Instrument cluster gauge function
• Instrument cluster warning lamp function
• Diagnostic trouble codes stored in all modules
• Range/inhibitor switch function (check for start in each detent)
• Any aftermarket accessories installed (interior or exterior)
• Manufacturer and any aftermarket technical bulletins or recalls

And with that, you'll have a leg up on discovering those weird problems...before the have you chasing ghosts.