Tire Monitor - Overview/Frequently Asked Questions
Information: IB08-08-S001Issue Date: JANUARY 2008
TPM System Overview, Diagnosing Tire Pressure Monitor System (TPM) Concerns And TPM Frequently Asked Questions (FAQ)
(This Bulletin Supercedes IB07-08-S002)
Affected Vehicles:
2007-2008 Isuzu Ascender
2008 Isuzu i-290/i-370 (TI)
Service Information
IMPORTANT:
The information found in this bulletin is designed to be a single source for the majority of questions you may have about the Tire Pressure Monitoring (TPM) Systems found on the above mentioned vehicles. While comprehensive, the bulletin is divided into sections, so after reviewing the whole document, you can reference just the section you need when further questions arise. A copy of this information may also be given to your customers as the "FAQ's" section is written to assist you in explaining the commen misconception about the system in an easy to understand way.
Customer Concerns and Confusion
When a customer comments on a condition related to tire pressure monitoring it is very important to distinguish between Check Tire Pressure/Low Tire Pressure conditions and Service Tire Monitor system issues. Understanding the difference between the two distinct conditions will help you distinguish between normal system operation (tire needs air) and a system malfunction. There are two important differences between a Check Tire Pressure/Low Tire Pressure message/light and a Service Tire Monitor message light:
^ A Check Tire Pressure/Low Tire Pressure message/light will stay on solid and no system codes are set. The TPM system is operating as designed. Correcting the tire pressure will resolve the issue.
^ A Service Tire Monitor message/light will blink and system codes WILL set. There is a condition that should be diagnosed and corrected.
Tire Pressure Light
Service Tire Monitor System (light blinks, then stays on)
The Tire Pressure Light will blink for about one minute and a Service Tire Monitor message will be displayed when a system malfunction occurs. For example: If one or more tire pressure sensors does not transmit information for 18 minutes of driving the TPM system WILL set a code display a message and BLINK the light for about a minute after which the light will stay on solid for the remainder of the ignition cycle. If the system fault is intermittent the message/light may also be intermittent - on during some ignition cycles off during others.
Low Tire Pressure Warning (light stays on solid)
If the TPM system detects a tire pressure below the threshold the Check Tire Pressure message and the Tire Pressure Light will come on and stay on. The message and light may be intermittent in nature especially during cold weather.
Conditions That Will Cause the Low Tire Pressure Warning Message/Light to Display:
^ The tire may have picked up a road hazard and/or have a slow leak.
^ The tire pressure may not have been checked in the past six months.
^ The air pressure in a cold tire may be at the pressure where the system is required to warn the driver. However that same tire will rise in temperature and pressure as the customer drives causing the message and light to go out.
^ The tires may have been rotated pressures adjusted and the new tire positions were NOT re-learned into the vehicle. This can occur on vehicles that have two different placard pressures for front and rear tires.
^ There may be a slow leak in one of the wheel and tire assemblies (Valve Stem Wheel Rim or Aluminum Wheel Porosity Leak). If this condition is found please refer to the Service Manual for further information.
Tire pressure should be set to the specified placard pressure at the lowest seasonal temperature the vehicle will encounter during operation.
The Effect of Outside Temperatures on Tire Pressures
IMPORTANT:
As a rule of thumb, tire pressure will change about 7 kPa (1 PSI) for every 6°C (10°F) decrease in temperature - dropping when it gets colder outside, rising when it gets warmer.
Tire pressure should be set to the specified placard pressure at the lowest seasonal temperature the vehicle will encounter during operation.
The correct action to avoid a Check Tire Pressure message due to extreme temperature changes is to do the following:
^ Use an accurate, high quality tire pressure gauge.
^ Re-learn the TPM sensors and adjust the tire pressure to the placard values after every tire rotation.
^ Let the vehicle sit and adjust the tire pressure to the specified value when the tire temperature is at the lowest expected temperature.
^ Never set the tire pressure below the placard value regardless of tire temperature or ambient temperature
IMPORTANT:
On extremely cold days, if setting the tire pressure when the vehicle has been indoors, it may be necessary to compensate for the low outside temperature by adding 21-27 kPa (3-4 psi) more then the placard pressure. At some later time, when convenient and when the tires are cold (outdoors), the pressure should be re-checked and adjusted to the placard pressures if necessary.
TPM Tool J 46915 Software Updates
The J 46915 TPM tool is a valuable aid in diagnosing system faults with TPM systems. It is a software-driven tool that REQUIRES periodic updates in order to work on new model vehicles. Failure to update the tool with the latest software version will result in possible misdiagnosis.
TPM Software Version 3.3 was released beginning with IDS version 9 and remains available on all current IDS software. Make sure TPM test tool J 46915 is up to date with the latest software. TPM version number is displayed when the TPMS tester is powered on.
Sensor transmission signal strength is displayed in the upper left corner of the main display next to the tool's battery level display. When the tool is used in both activate or scan mode it will receive the sensor's transmission and indicate its signal strength. It is important to note the sensor's transmission signal strength since it is a good indication of an accurate diagnostic.
Diagnostic Tip
The placement of the TPM Tester's antenna when activating a sensor is critical especially with the latest software update installed. When activating a sensor the antenna tip of the TPM Test J 46915 must be placed on the sidewall perpendicular to the tire and close to the valve stem (see photo). This will assure proper activation of the sensor. If the antenna of the TPM Tester is placed either on the valve stem or on the wheel itself the tool may not properly activate the sensor causing improper diagnosis.
One of the steps in the TPM diagnosis is to use the J 46915 and the Tech2 to verify that the sensor IDs are programmed into the vehicle in their correct locations.
Diagnostic Tip
If you encounter a sensor that does not respond when activated by the tool try activating another sensor that responded previously. This will help you determine if the tool is able to activate the sensor or if you have a problem with one particular sensor.
IMPORTANT:
A sensor that does not transmit information for 18 minutes of driving will set a TPM system DTC.
Diagnostic Tip
When using the tool during a sensor learn procedure use the "Activate" soft key on the tool. Press the key for one second then release and the tool will perform an LF (low frequency - 125 kHz) activation cycle. You do not have to hold the key until the vehicle acknowledges. Holding the key will just reduce battery life. The LF activation of the sensors wakes them up and forces them to transmit their IDs immediately. This allows a much shorter sensor learn procedure than using the Delta P method.
TPM Frequently Asked Questions (FAQ's)
The images above are of the most asked questions.
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