What does it mean?
P1648 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Glow Plug Module Internal .
Symptoms
- MIL on and usually the glow plug (preheat) lamp lit or flashing on the cluster
- Hard cold starting and extended cranking, especially in cold weather
- White or blue smoke and rough running for the first minute after a cold start
- Misfire and shaking until the engine warms up
- Little or no symptom in warm weather, so the fault seems to come and go seasonally
Likely causes
- Internal failure of the glow plug module output stage
- Water and corrosion in the module connector; the unit often sits low in the engine bay
- A shorted glow plug dragging one output down and overloading the module
- Chafed or heat-damaged glow plug harness shorting to the cylinder head
- Weak battery, poor high-current feed or a corroded heavy ground at the module
- Blown high-current glow system fuse or fusible link
- Module overheating after repeated long preheat cycles in cold weather
How to fix it
- Scan for companion glow plug circuit codes to see whether one cylinder or the whole module is flagged
- Check the glow system fuse or fusible link, then measure the module power feed and heavy ground with the ignition on
- Unplug and inspect the module connector for water, corrosion and burnt terminals
- Measure the resistance of each glow plug and replace any that is shorted or open; a shorted plug can destroy the module
- Inspect the harness from the module to the plugs for chafing against the head and heat damage
- Test the battery and charging voltage, since low voltage upsets the glow control strategy
- Replace and, where required, program the glow plug module only after the plugs and wiring are proven good