How does the Low tire pressure warning system work? Sorry for a newbie question, I just can't figure this one out.

 

When psi drops below 28psi, Dash light comes on

bart

 

There is a pizoelectric component attached to a metal band that goes around the rim center before the tire is installed.(or after but before sealing) it has a sensor that sends a signal as the tire rotates. if the pressure falls above the 28 psi, the signal is picked up by the reciever and turns on the light. there is a different frequency for each wheel and the DIC codes can tell you which wheel has the low pressure.

 

how do you read the dic codes?

 

You use the ALD connector under the dash. what year car do you have. email me and I can send you some pics with the directions.



[Modified by C4TOMCAT, 6:51 PM 8/23/2002]

 

'89 was the first year and there are no codes as the '89 receiver does not communicate with the ECM. System consists of a Receiver (mounted behind the passengerside of the dash and it gets its hot lead and ground from the Passkey Module) and 4 individual wheel sensors. Sensors generate two radio like or electronic signals and are powered up by the vibrations of the moving wheel in which they are mounted. The first is a diagnostic which tells the Receiver the sensor is working and the second is the low pressure signal which is generated by a switch within the sensor which is set to go off when pressure falls below 25 psi. Vehicle has to be moving about 25 mph for 30 seconds for a sensor to power up & generate a signal. '89 Shop Manual procedure for diagnosing a wheel sensor is to apply an air hammer to the bottom of the tire with the valve stem of the wheel pointing forward. If the warning light illuminated, the sensor was supposedly bad. Receiver failures and false alarms seem very common with the '89 system. I read an article somewhere (I think VETTE magazine) that the early Receiver wasn't very well shielded and will generate a false signal from allmost any electrical noise (including that coming from other cars idling next you in traffic). Receiver failure will generally show up as an illuminated light with the vehicle at a standstill. Receiver is no longer made and used ones are questionable. Wheel sensors seem to last but are commonly broken by careless removal and installation of tires. For '89, the factory affixed a round sticker to each wheel indicating it's mounting postion & sensor (RF, LF, RR, LR) and the owner's manual instructed that the sensor had to remain in it's indicated position for the system to work (so if you wanted to rotate tires, you needed to dismount the tires). GM subsequently issued a TECH BULLETIN stating that '89 sensor position didn't matter and that tires could be rotated in a normal manner. Sensors are mounted opposite or 180 degrees from valve stem. '90 and up models should have a decal on the inside of the rim indicating mounting position of the sensor and later models communicate diagnositic codes via the serial data line from the ECM.

 

Thanks for the info. :yesnod:

 

One oddity to the system (at least on the '89 - mebbe on other years as well). If all four sensors are defective or missing, the "Check system" light will not go on. If one to three sensors are defective or missing, the trouble light will illuminate. :confused:

Rich