Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2009TAHOE BASE, 4.8 CREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 6 (HYBRID ENERGY STORAGE SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESJUMP ASSISTCHARGING PROCEDURE
2009 Chevrolet Tahoe Base, 4.8 C
Charging Procedure
2009 Chevrolet Tahoe Base, 4.8 CSECTION Charging Procedure
WARNING: This page is about a different variant/trim than selected.
- Turn the ignition key to the RUN position.
- Observe and record the BECM Hybrid Battery Pack Calculated voltage scan tool parameter. You should observe greater than 194 volts.
- If the voltage is less than 194 volts, Jump Assist will not initiate and the drive motor generator battery must be replaced. Refer to Drive Motor Generator Battery Replacement .
- Observe and record the APM HPCM 300 V Circuit voltage scan tool parameter. Compare the BECM Hybrid Battery Pack Calculated voltage value to the HPCM 300V Circuit voltage parameter. You should observe both parameters are within 30 volts.
- If the parameters are not within the specification, the high voltage contactor relays have not closed. Diagnose the DTCs that have opened the high voltage contactor relays. Refer to Diagnostic System Check - Vehicle (with HP2) .
- Upon activation of Jump Assist, the Driver Information Center (DIC) display will transition from the current message such as "HOOD OPEN" to "JUMP ASSIST READY TURN KEY OFF". Do not turn the ignition OFF without first turning OFF the scan tool or the procedure may fail to initialize. Perform the following steps in exact order:
- Initiate the APM Jump Assist output control with the scan tool. You should observe the READY message on the DIC.
- Turn the scan tool OFF.
- Turn the ignition key to the OFF position.
- Jump Assist will initiate and a transfer of energy between the 12 volt DC battery charger and the drive motor generator battery will occur through the APM. The DIC should display "JUMP ASSIST ACTIVE BATTERY CHARGING".
- While leaving the ignition OFF, turn the scan tool ON and observe the BECM Calc. Hybrid Batt. Current parameter. Estimate the total amount of time for a successful Jump Assist using the Jump Assist Current vs. Time table shown below.
- Continue with Jump Assist until the estimated time has elapsed or the DIC displays either JUMP ASSIST COMPLETE or JUMP ASSIST ABORTED.
- If the estimated time has elapsed or the DIC displays the "JUMP ASSIST COMPLETE" message the drive motor battery should have sufficient charge to start the engine.
- If the DIC displays the "JUMP ASSIST ABORTED" message, one of the following conditions has occurred. Repair the condition and restart Jump Assist if necessary.
- The 12 volt circuit was not maintained at greater than 11.0 volts
- The HPCM stored a DTC which resulted in the opening of the high voltage contactor relays
- The drive motor generator battery voltage is greater than 358 volts or less than 180 volts
- The ignition key was turned to the RUN position while the Jump Assist output control was active
- Turn the ignition ON. The DIC may display JUMP ASSIST ABORTED.
- Attempt to start the engine.
- If the engine cranks and runs, drive the vehicle for at least 20 minutes to allow the BECM to relearn drive motor battery state of charge.
- If the engine does not crank, refer to Engine Will Not Crank .
NOTE:
The scan tool may be removed from the vehicle at this time if desired and the Jump Assist will continue.
Jump Assist Current vs Time
| Calc. Hybrid Battery Current (Amps)* | Time (Minutes) |
|---|---|
| 0.25 Amps | 228 minutes |
| 0.50 Amps | 114 minutes |
| 0.90 Amps | 63 minutes |
| 1.40 Amps | 41 minutes |
| 1.90 Amps | 30 minutes |
| 2.40 Amps | 24 minutes |
| 2.90 Amps | 20 minutes |
| *Depending upon model year, hybrid battery current may be displayed as a negative value when charging during Jump Assist. | |
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.