2008 Mack Granite - Erratic Gauges and Engine Cutting Out

Question

I've got an old 2008 Mack Granite dump truck that is giving me an electrical nightmare. While driving, all the gauges on the dash will suddenly drop to zero, the 'Warning' light comes on, and the engine will stumble or even cut out for a second. Then it all comes back to life and drives fine for another ten miles.

I suspect a bad ground or a J1939 data link issue. I've looked at the wiring under the dash and behind the instrument cluster, and nothing looks obviously frayed. I've also checked the battery connections and the starter grounds. It seems to happen more often when I hit a bump in the road.

BoostedBryan · Accepted Answer

✅ Confirmed fix: The issue was the main power supply wire for the ECM where it routes through the battery box. The insulation had rubbed through against the frame rail, causing a momentary short to ground whenever the truck hit a bump. This would kill the J1939 communication and the ECM power simultaneously. Patched the wire and secured the loom away from the frame.

HighwayHelen · Answer

Check the 14-pin connector at the bottom of the fuse box. These are known for getting corrosion which interrupts the power to the VMAC (Vehicle Management and Control) system. A little green crust in there can cause all the symptoms you're describing.

2008 Mack Granite - Erratic Gauges and Engine Cutting Out

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