Symptoms
A turbo diesel that stalls when hot and restarts once it cools, then gets harder to restart as the fault worsens. Codes P0251 and P0370 point at the injection pump's optical sensor and the PMD. A fuel shutoff solenoid problem is different: it sputters before stalling.
The fix, step by step
- First rule out fuel: change the filter, check the lift pump and look for a kinked return hose.
- The Stanadyne DS4831 pump on 1996–2004 turbo diesels carries its electronic driver (PMD, also called FSD) on the pump itself, in the engine's heat.
- Fit a new PMD on a remote heat sink outside the engine bay, with thermal paste and the extension harness.
- If codes persist, have a Stanadyne shop check the pump; Flash Off-Road says to fit a DS4831-5288 or -5521, not the early -5067.
Tools & part numbers
- Torx and socket set
- thermal compound
- scan tool to read and clear codes
- Stanadyne fuel additive
Where to buy the parts
Fuel pump drive module (PMD), 1998 H1 6.5 TD (catalog)RockAuto ↗
PMD relocation kit, 1998 H1 6.5 TD (catalog)RockAuto ↗
H1 RapCool High Performance PMD IsolatorPredator Inc ↗Amazon ↗
Hunting a used or discontinued part? Search eBay Motors for AM General Hummer H1 parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.