OBD-II trouble code
P0676: Cylinder 6 Glow Plug Circuit
A fault on the cylinder 6 glow plug channel. On the inline-six diesels where this code lives, cylinder 6 sits at the far end of the feed, and that distance is the whole story: a glow plug draws serious current, so the test that matters is voltage under load, not a continuity beep.
Quick facts
- System
- Powertrain
- Category
- Auxiliary Emissions Controls
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $40 – $900
- DIY difficulty
- Intermediate DIY
What does P0676 mean?
P0676 means the glow plug control module found something wrong with the cylinder 6 channel during preheat. The candidates are the usual four — the heating element, the terminal, the wire feeding it, or the module's own output stage — but which one you look at first should be decided by a fact about this particular channel rather than by working down a generic list.
Cylinder 6 exists on inline sixes, V6 diesels, V8s, V10s and V12s. The inline six is the classic case and the one this page is built around, because it is where cylinder 6 has a specific electrical disadvantage: **it is the last cylinder in the row, so its feed is the longest run in the glow harness.** Whatever supplies the plugs — a bus bar strip laid along the head, or individual branches from a controller mounted at the front of the engine — cylinder 6 is at the end of it.
That matters because of how much current a glow plug takes. This is not a sensor circuit carrying milliamps. A cold glow plug is a very low resistance element, and at the instant it is energised a single plug can pull well into double-digit amps before settling as it heats. Six of them together represent a serious load. **Under that kind of current, a small amount of unwanted resistance stops being invisible and starts eating volts.**
Here is the practical consequence, and it is the reason people replace a good plug on this code. A corroded terminal, a partially broken strand bundle, or a bus bar nut that has lost its clamping tension will still show continuity. Put a meter across it with no current flowing and it beeps, reads a fraction of an ohm, and looks fine. Energise the system and the same joint drops a volt or two, the plug at the end of the run gets meaningfully less than the others, it heats more slowly, its current profile falls outside what the module expects, and the module logs cylinder 6. The plug is healthy. The joint is not.
So the test to run here is a **voltage drop measurement taken while the glow circuit is actually energised.** Trigger a preheat cycle on a cold engine and measure at the cylinder 6 plug terminal, against a good engine ground, during the few seconds the plugs are live. Compare that with battery voltage and, better still, with what the plug at the other end of the run is seeing. A meaningful difference between the near plug and the far plug points squarely at the connection path rather than at the element.
One more inline-six specific: many of these engines feed the plugs through a common bus bar or connector strip that runs the length of the head, held on each plug stud by a small nut. The end terminal of that strip is the one with the least mechanical support, the most thermal movement to absorb, and the greatest chance of having been left slightly loose the last time someone worked on the engine. Before condemning anything, take the strip off, look at the cylinder 6 stud and terminal for discolouration and green corrosion, clean it properly, and refit it to the correct torque.
Common causes
- High-resistance joint at the cylinder 6 terminal — corroded, loose or heat-discoloured — dropping voltage under load while still reading continuous
- Bus bar or connector strip nut that has lost clamping tension at the end plug
- Cylinder 6 glow plug element open or drifted high with age
- Long branch wire to cylinder 6 with broken strands inside intact insulation
- Corroded or undersized ground path serving the glow circuit, exaggerated at the far end of the run
- Weak battery or poor main supply connection, which drops hardest on the longest branch
- Failed cylinder 6 output channel in the glow plug control module
- Previous repair that left the strip refitted loose or the terminal reused after corrosion
- Mixed plug specifications after a partial replacement, so the module sees inconsistent current draw
Symptoms
- Extended cranking on cold starts, more pronounced as ambient temperature drops
- Rough idle or a brief misfire on one cylinder for the first minute after a cold start
- White smoke from cold that clears as the engine warms
- Check engine light with P0676 stored, sometimes with an adjacent cylinder code
- The fault appearing intermittently — worse after damp weather or a wash, better when dry
- A glow plug replaced on this cylinder recently that did not fix anything
- No abnormal behaviour once the engine is warm
Diagnostic steps
- 1.Read all stored codes. If several channels report together, look at the shared supply, ground, relay and fuse before testing individual branches.
- 2.Establish where the glow plug controller or supply point sits on this engine and trace the run to cylinder 6, because the length of that run is the argument this diagnosis rests on.
- 3.Remove and inspect the bus bar or connector strip if the engine uses one, giving particular attention to the terminal on the cylinder 6 stud — look for discolouration, green corrosion and a nut that turns too easily.
- 4.Measure resistance at every plug terminal and compare across the engine. Matched low readings with one outlier identifies a failed element.
- 5.If the resistances all match, do not stop there. Trigger a preheat on a cold engine and measure voltage at the cylinder 6 plug terminal while the circuit is live.
- 6.Compare that live voltage against battery voltage and against a plug at the opposite end of the run. A significant shortfall at cylinder 6 alone points at the connection path, not the plug.
- 7.Wiggle-test the branch and connector during the energised window if the fault is intermittent, since a broken strand bundle can make and break under vibration.
- 8.Check the engine-to-body and battery ground connections under load; a marginal ground affects the far end of the run first.
- 9.Clean and correctly torque every terminal you disturb, then re-test rather than assuming the cleanup worked.
- 10.Confirm the repair after an overnight cold soak — the module only tests this circuit during preheat, so a warm restart proves nothing.
Repair cost
$40 – $900
Diagnosis is $80 to $180 and is worth paying for here, because a clean terminal is a $40 fix and a plug is not. Cleaning and re-torquing a corroded bus bar terminal is often $40 to $150. A replacement bus bar or connector strip is $40 to $200 plus about an hour. A single glow plug is $120 to $400 fitted depending on access; on an inline six with a rear plug under intake pipework or a turbo feed, $300 to $650. Branch wire repair is $90 to $260. A glow plug control module is $250 to $750 fitted. A full set of six is typically $150 to $450 in parts, which is often the right call once the strip is already off.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with wiring harness / circuit repair preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.