P0382
PowertrainGlow Plug/Heater Circuit "B"
On a cold morning you turn the key, the 'Wait to Start' light hangs on longer than usual, and the engine cranks and cranks before it catches, often coughing out white smoke before it settles. That's what P0382 feels like from the driver's seat. The ECM watches the glow plug heater circuit, and on this code it's flagging the second circuit (the 'B' bank) for being out of range or not responding the way it expects. The plugs are what warm the combustion chambers so a diesel will light off when it's cold, so when one circuit drops out your cold starting suffers.
ⓘ Information only. This page provides general educational information about fault code P0382. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0382 mean?
P0382 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Glow Plug/Heater Circuit "B".
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Hard starting first thing in the morning or after the car's sat overnight, much worse below freezing
- • The 'Wait to Start' glow plug lamp staying lit far longer than the usual second or two
- • White smoke from the exhaust for the first minute or so until it warms up
- • Rough idle or a stumble right after a cold start that smooths out once the engine's up to temperature
- • Engine warning light on the dash
- • Slightly worse fuel economy in cold spells while the engine struggles to run clean from cold
Possible causes
Causes commonly associated with P0382, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. A single failed or burned-out glow plug on the 'B' circuit. The most common cause by a mile, plugs wear out and an open one will trip this code
- 2. Corroded or loose wiring and connectors at the glow plug feed, the spade terminals on top of the plugs go green and brittle over time
- 3. Blown fuse or a tired glow plug relay that isn't feeding the circuit properly
- 4. A faulty glow plug control module on engines that use one, common on later VAG and BMW diesels that monitor each plug individually
- 5. Poor earth or a high-resistance connection somewhere in the circuit throwing the resistance reading off
- 6. ECM fault, rare, only suspect this once everything upstream checks out clean
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Pull the glow plug terminal caps off and test each plug on the 'B' circuit for resistance with a multimeter. A healthy plug reads very low, usually well under 1 ohm. Anything open or sky-high is dead
- 2. Have a proper look at the wiring and the spade connectors on top of the plugs for corrosion, melting, or a cap that's worked loose. This is where a lot of these faults actually live
- 3. Check the glow plug fuse and relay, swap the relay for a known-good one if you can to rule it out cheaply
- 4. On engines with a glow plug control module, scan it for its own codes and check the feedback voltages it's reporting back to the ECM
- 5. Note any other stored codes at the same time. A spread of glow plug faults pointing at multiple cylinders usually means the module or wiring rather than a single dead plug
- 6. Clear the codes after the repair and do a cold start the next morning to confirm it stays gone
Common questions about P0382
How do I know if it's an actual glow plug gone or just dodgy wiring? +
Test the resistance of each plug on the circuit first. A good plug reads under 1 ohm, an open or failed one reads as no continuity at all, and that points straight at the plug. If the plugs all test fine but you're still getting the code, the fault is in the loom, the spade connectors, or the relay. The connectors on top of the plugs are the usual troublemakers, they corrode and crack. Wiggle them while testing and watch for the reading jumping around, that tells you it's a connection rather than the plug itself.
How long does this take to put right at a garage? +
A single plug that comes out cleanly is an hour or so of labour, and a relay or fuse is quicker than that. The catch is seized plugs. On a high-mileage diesel that's never had them touched, a stuck plug can take an afternoon to extract safely, and if one snaps the head it can mean removing the lot and using extraction tools or even pulling the glow plug to do it properly. Budget for that possibility if your car's done big miles and the plugs are original.
Are cheap glow plugs worth fitting or should I pay for the branded ones? +
Stick with a known brand like Bosch, NGK, or Beru on glow plugs. The cheap eBay sets fail early, sometimes within a year, and on engines that monitor each plug a poor-quality one can set this code straight back up. The price difference per plug is small, maybe a few pounds each, and it's not worth doing the job twice. If you've got an awkward engine where access is a pain, fit a full set of good plugs while you're in there rather than chasing them one at a time.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →