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 MANUALSCHEVROLET2008CHEVY EXPRESS G3500, VAN PASSENGER EXTENDEDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 986 (AUTOMATIC TRANSMISSION - 2ML70 - SPECIFICATIONS)SPECIFICATIONSTRANSMISSION INTERNAL MODE SWITCH LOGIC
2008 Chevrolet Chevy Express G3500, Van Passenger Extended
Transmission Internal Mode Switch Logic
2008 Chevrolet Chevy Express G3500, Van Passenger ExtendedSECTION Transmission Internal Mode Switch Logic
WARNING: This page is about a different car, the 2012 GMC Yukon, 2012 Chevrolet Tahoe, and 2012 Cadillac Escalade. However, it is still accessible from the selected car via links, so may be relevant.
Internal Mode Switch (IMS)
| IMS Circuits/Parameter | Selector Position | ||||
|---|---|---|---|---|---|
| Park | Reverse | Neutral | Drive | Manual | |
| Direction Switch Operating Conditions: Ignition ON, range selector in appropriate gear | |||||
| Direction IMS D1 | HIGH | HIGH | LOW | LOW | LOW |
| Direction IMS D2 | LOW | LOW | HIGH | HIGH | HIGH |
| Direction IMS R1 | HIGH | LOW | LOW | HIGH | HIGH |
| Direction IMS R2 | LOW | HIGH | HIGH | LOW | LOW |
| Direction IMS Start | LOW | HIGH | LOW | HIGH | HIGH |
| Range Switch Operating Conditions: Ignition ON, range selector in appropriate gear | |||||
| IMS A | LOW | LOW | HI | HI | HI |
| IMS B | HI | LOW | LOW | LOW | HI |
| IMS C | HI | HI | HI | LOW | LOW |
| IMS P | LOW | HI | LOW | HI | LOW |
| Always HIGH status: Open/short to voltage condition Always LOW status: Short to ground condition Every status HIGH for either switch indicates an open ground circuit or connector for that portion of the IMS. |
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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.