P0382: Glow Plug Circuit B Malfunction - Causes, Fixes & Cost [2026]
What is P0382? P0382 is set on diesels that use two glow plug relays (one per bank on V-diesels, or staged firing on some I-6s). The "B" circuit failed to respond when commanded - relay fault, wiring break, or a group of glow plugs with high resistance.
🎯 Top 3 Causes Ranked by Probability
52%
#1 - Most Likely
Failed Glow Plug Relay (Bank B)
The high-current relay for bank B has burned contacts or an open coil. Most common cause on V-diesels.
🔨 Part
$50-$220
👨🔧 Labor
$60-$200
⚡ DIY
Easy
33%
#2 - Check First
One or More Bad Glow Plugs (Bank B)
A shorted plug pulls the bank to ground; an open plug breaks the current path. Resistance-test each plug.
🔨 Part
$80-$350
👨🔧 Labor
$150-$600
⚡ DIY
Medium
15%
#3 - Less Common
Wiring/Connector Fault
Heat damage near the manifold or a corroded connector on the bank B feed wire.
🔨 Part
$10-$80
👨🔧 Labor
$80-$250
⚡ DIY
Medium
🔧 Step-by-Step Diagnosis
- Check for companion codes - P0380, P0671-P0678, or P0673-P0680 will pinpoint individual cylinders.
- Locate the bank B glow plug relay. Most Ford and GM diesels have two relays mounted near the intake manifold.
- Key on, listen for the relay click. No click means the relay coil or its control wire is bad.
- Test each bank B glow plug for resistance - spec is usually 0.5-3 ohms. Replace any out of spec.
- Inspect the feed wire from the relay to the glow plug bus bar for heat damage or breaks.
🚗 Most Affected Vehicles
🚫 Is It Safe to Drive with P0382?
Hard cold starts and white smoke until fixed. Driveability is fine once running, but cold-weather starts can fail.
❓ Frequently Asked Questions
What does Circuit B mean in P0382?
On V-configuration diesels with two glow plug relays, A is one bank/group and B is the other. Circuit B is the second relay and its plugs.
Will my diesel start with P0382?
In warm weather, yes - the engine does not need glow plugs once it is above about 50F. In cold weather, expect hard starts, smoke, and a rough first minute.
Can I replace just one glow plug?
You can, but most experienced diesel techs replace them as a set. Glow plugs that have shared service life often fail in sequence.
How long do glow plugs last?
Typically 80,000-120,000 miles. High-pressure common-rail diesels with two-stage glow systems sometimes stretch to 150k+ miles.
Is the glow plug relay expensive?
Most are $40-$150 in parts and 30-60 minutes of labor. On the Ford 6.0L Power Stroke the dual GP relays are a known wear item and a cheap fix.