Low Tire Light On And / Or DIC Check Tire Pressure Message When Cold - keywords air MIL monitor program wheel

This PI was superseded to update models and model years. Please discard PIT3569B.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

The TPM system is required by law to warn the driver if the tire pressure is below 25% of the tire pressure displayed on the tire placard. It is possible to have one or more cold tires at the trigger point and when warmed up during operation exceed the trigger point. As a rule of thumb, tire pressure will increase 1 psi (6.8 kpa) for every 10 degrees F (5.5 degrees C).

Example:

A 2005 Yukon has a tire placard value of 30 psi (206.8 kpa) cold. The customer drives the truck for several miles to get to the service station and the tire temperature is 65 degrees F (18.3 degrees C) when the tire pressure is adjusted. Unknowingly, a pencil style pressure gage that reads 3 psi (20.6 kpa) higher than actual pressure is used.

The vehicle sits outside at night and the ambient temp drops to 20 degrees F (-6.6 degrees C). The actual tire pressure in the morning is 22.5 psi (155.1 kpa), which is right at the borderline where the system is required to warn the driver of low tire pressure.

The customer drives away in the morning and notices a "Low Tire Pressure" message and a Low Tire indicator warning light. The light goes out after several miles of driving and the customer does not see the message again until the next morning. The customer thinks there is a problem with the TPM system because they just had the tire pressures checked.

Two things are vitally important in the above example.

The tire pressure should be set to the specified pressure at the lowest temperature the vehicle will be operated. Remember tire pressure goes up 1 psi (6.8 kpa) for every 10 degrees F (5.5 degrees C). If you are unsure of tire temperature when you are adjusting pressure, use an infrared temperature tool. If you have a tire temperature of 60 degrees F (15.5 degrees C) and you expect the ambient temperature to reach 20 degrees F (-6.6 degrees C) at night, add 4 psi (27.5 kpa) to the 30 psi (206.8 kpa) and set the tire to 34 psi (234.4 kpa) at 60 degrees F (15.5 degrees C).

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.