Difficult Cold Start
Several things could be causing difficult cold starts for your 6.6L Duramax:
Problem: Poor fuel quality
Solution: Treat with Diesel Extreme to improve fuel quality.
Problem: Glow-plug problem
Solution: Check glow-plugs.
To check the glow plugs:
1. Look at all the wiring leading to the glow plugs for breaks or cracks in the insulation. Each glow plug should have 4.7 V going to it during the glow-plug cycle.
2. If the wiring and voltage are good, measure the resistance across the glow plug to see if it within specification.
Anything over 1 ohm is too much resistance.
An “OL” reading on your DMM means there is no continuity in the circuit, and the glow plug is bad.
An individual glow plug problem will be associated with a DTC ranging from P0671-P0678.
Occasionally, the glow plug controller module itself can be defective and needs to be replaced.