Diagnosing Diesel Concerns
Diagnosing Diesel Concerns
Hard start cold
Glow plug system first. Test each plug individually for resistance — typically 0.5 to 2 ohms. Open circuit means failed. Verify the glow plug controller is commanding the plugs on during the preheat cycle — measure voltage at the supply bus. If all plugs test good and the controller commands correctly — check fuel quality, check for air in the fuel system, and verify the low-pressure fuel supply is adequate.
Smoke diagnosis
Black smoke — over-fueling or restricted air intake. Check the air filter. Check the turbo for boost issues. White smoke on a warm engine — coolant entering combustion. EGR cooler failure or head gasket leak. Check coolant level and perform a cooling system pressure test. Blue smoke — oil in combustion chambers. Check turbo shaft seals and oil drain line.
DPF regeneration
Before replacing a DPF — perform a forced regeneration with the scan tool first. Many DPF concerns resolve completely with a successful regen at a fraction of the replacement cost. A vehicle used exclusively for short urban trips may never achieve temperatures for passive regen and loads up with soot. A forced regen burns the accumulated soot.
Never expose any body part to a suspected diesel fuel leak at operating pressure. Modern common rail systems operate at 20,000 to 30,000 PSI. These pressures penetrate skin and cause injection injuries that are medical emergencies. Use cardboard to detect leaks — never your hand.