Diagnostic Aids
WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
- If the vehicle is equipped with an auxiliary battery (TP2), verify that there is not a fuse installed in the STUD 1 Fuse 70 position of the underhood fuse block. A plastic plug may be installed in this position instead of a fuse. If a fuse is installed in this position and any optional equipment is powered by the auxiliary battery, it will discharge the primary battery in addition to the auxiliary battery.
- Verify that all accessories are turned OFF, including optional accessories that the vehicle may have been wired for, but does not have installed, such as auxiliary lights. If an optional accessory swich is left in the ON position, it may energize a relay that will discharge the battery over time, even if the accessory is not installed on the vehicle.
- Be sure to rule out any possible obvious influences, such as customer error or aftermarket equipment. Anytime aftermarket accessories are installed into the courtesy lamp circuit, it can cause the inadvertent power timer in the body control module (BCM) to keep resetting. This would cause the BCM to remain awake and cause a current drain on the battery.
- Customer driving habits, such as regular short trips. This does not allow enough time to properly charge the battery. Refer to Battery Description and Operation .
- Verify that the battery and charging system are in proper working order. Refer to Battery Charging and Charging System Test .
- A battery discharging for no apparent reason while the vehicle is parked can be caused by an intermittent draw, such as a module waking up, or a continuous draw, such as a dome light or stuck relay. Look and listen for any components that may be operating when they should turn off, such as a fuel pump.
- Some systems and modules such as OnStar®, and regulated voltage control (RVC), if equipped, are designed to wake-up, perform a task, and go back asleep at regular intervals. Refer to Body Control System Description and Operation for the system or modules description and operation.
- Remote keyless entry (RKE) will wake up due to an outside input. Refer to Keyless Entry System Description and Operation for the system description and operation.
- The battery run down time will vary depending on cold cranking amperage (CCA) and reserve capacity (RC). If the CCA and RC are higher, then the battery run down time would be longer. If the CCA and RC are lower, then the battery run down time would be shorter. The graph below indicates roughly how many days a 690 CCA battery with at 110 min. RC (60.5 AH) starting at 80 percent state of charge will last with a constant current draw until it reaches 50 percent state of charge. Differences in battery rating and temperature will affect the results.
IMPORTANT:
The battery specification listed below is a generic specification. Refer to Battery Usage when testing the battery.
| Current Drain | Days |
|---|---|
| 25 mA | 30.5 |
| 50 mA | 16.5 |
| 75 mA | 11 |
| 100 mA | 8.25 |
| 250 mA | 3.3 |
| 500 mA | 1.65 |
| 750 mA | 1 |
| 1 A | 0.8 |
| 2 A | 0.4 |