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A practical guide to TPMS

Thursday, November 2, 2017 - 07:00
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To do this, it’s important to replace seals or other parts as directed in service information (or required because they’re obviously not fit for re-use) and also to be careful not to over-torque and damage the somewhat delicate TMPS components. This is important.

It’s not just important because over-torqueing breaks and warps things, which causes immediately noticeable problems, it’s also an important step because it prevents future problems from ever developing.

Leaks and breaks are fairly common so it’s wise to keep this in mind when working in the area. It’s better to prevent problems from occurring than to have to fix them later.

Repairs

Servicing the tire pressure sensors themselves (either because the tires are being changed or the sensor needs replacing) is usually straightforward and relatively simple but there are a few practical tips to keep in mind to keep the work problem-free.

This is rare but it did happen and it’s worth noting. This customer bought rims with the wrong size valve stem holes and the TPMS sensor wouldn’t fit. So the customer drilled another hole and installed a dummy valve 180 degrees from the working sensor. It’s still working.

Typically when replacing a TPMS sensor the tire is deflated and the retainer is unscrewed and the sensor then drops gently into the wheel. Then the tire is removed, the sensor is re-installed (with new seals or components) or replaced as required, and then the tire is re-installed and inflated, installed on the vehicle and then programed and relearned as required.

However, there are ways to keep this routine task both quick and problem-free.

One important thing to keep in mind is that not breaking the sensor off during service can actually be a bit tricky. Some manufacturers use metal valve caps on the sensors and unfortunately these can seize to the stems which can then break off when they’re removed (often with pliers) for routine service – not good at all.

Also, it’s important to know if the gasket and seals on the sensor will indeed need to be replaced, and if so to have them ready to use. The reason for this is obvious, seals often can’t be re-used and it’s good to have the replacements on hand so that new leaks aren’t created in the wheel. Again, the valve area is a notoriously common leak spot and it’s important to prevent this problem if at all possible,

This tire label got caught between bead and rim of this Lexus tire and caused a very tiny leak (less than half a psi every 300 miles). This would have likely gone unnoticed but the tire pressures were displayed at each wheel and the customer was fanatic about keeping the pressures equal. Resealing the wheel (after removing the sticker) fixed the problem

Finally, it’s important to make sure any manufacturer stickers are removed from the tire before it’s installed so the bead can seal to the rim thoroughly – not doing so can and does cause problems.

One Lexus customer brought their vehicle in because the pressure at a particular wheel would drop by 1 psi each week (all four wheel pressures were displayed so the difference was very noticeable). Turns out when new tires were installed the bar code sticker was never removed from the bead of the tire and there was indeed a small leak between the sticker and the rim. The wheel had to be broken down, resealed, and reinstalled to fix the problem.

Troubleshooting tips

Usually when the TPMS warning light illuminates the fault is repaired by sealing a leak, correcting tire pressures, patiently performing a relearn procedure, or by replacing a faulty sensor (or a combination of all these things).

However, as with any routine diagnosis, it helps to keep a few things in mind to prevent problems from developing.

As with any other troubleshooting, it’s important to start TMPS diagnosis by verifying that there actually is a problem and that the bulb comes on during bulb check and then goes off.

If there is actually is a problem, check all tire pressures, and adjust them if necessary, keeping in mind that it may take a few moments for the data to refresh and display accurately. Adding or removing air a little bit of air at a time tends to be the quickest way to get good results.

One important tip to keep in mind that using clean, dry air is very important – air lines that spray water everywhere can get water inside the TPMS sensor and cause problems to develop. One excellent tech I worked with insists that water from air lines damages more TPMS sensors than those spray cans of tire sealer and inflator ever will.

Continuing on, if a low tire is indeed present, be sure to also inspect the condition and wear patterns of all the tires in case they need to be replaced – and also because it’s better to notice exposed belts and sharp, damaged rims at this stage rather than when they go through your hand during service. It’s definitely better to find out early on if extra work is needed or if extra caution will be required during the repair.

If everything checks out okay but the system still indicated a tire with low pressure make sure the control module is seeing the sensors and receiving the data OK. It’s not uncommon for one sensor (or more) to be faulty and not send information to the control module. The sensors themselves have batteries that usually last for just over five years and the batteries aren’t replaceable – the whole sensor is replaced and subsequently programmed when the battery fails.

Metal valve caps – like this one – have been known to seize to the valve stem and undoing them with pliers can actually break the sensor. Best to prepare the customer beforehand if there’s any chance of damage during service and be sure to torque caps correctly.

Also, since the warning light is often controlled by the body control module, check that all of the fuses are good (most vehicles have several fuse centers that need to be checked) and note any other problems in the system such as aftermarket accessories or systems that interfere with electrical signals. Some sensors are sensitive to interference from other sensors and systems. In fact, some Toyota vehicles have QR stickers on the rim so that the techs can simply scan the code with the tool and program the sensor that way which is quicker and also prevents interference from being an issue (the stickers are supposed to be removed at PDI but have been known to be left in place). Checking for service bulletins or tech tips on this issue can definitely save diagnostic time.

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