OBD-II trouble code
P0675: Cylinder 5 Glow Plug Circuit
A fault on the cylinder 5 glow plug channel. The number itself is the first piece of evidence: a fifth cylinder rules out the four-cylinder diesel most glow plug advice is written for, and the engine it does point at changes the parts list, the access and the price.
Quick facts
- System
- Powertrain
- Category
- Auxiliary Emissions Controls
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $70 – $950
- DIY difficulty
- Intermediate DIY
What does P0675 mean?
P0675 reports a fault on the cylinder 5 branch of the glow plug system. The glow plug control module energised that channel during preheat, measured the current that flowed, and did not get the answer it expected — usually an element that has gone open or drifted high in resistance, sometimes a terminal, a branch wire or the module output itself.
Before any of that matters, notice what the code has already told you. **Cylinder 5 exists, so this is not a four-cylinder engine.** Almost every glow plug article, forum thread and parts listing on the internet is written around the four-cylinder diesel, because that is what most of the world drives. P0675 is the first code in the per-cylinder series that cannot come from one, and that single fact reshapes the job.
The realistic candidates are an inline five, an inline six, or a V-configuration diesel of six cylinders or more. The inline five is worth calling out because it is a genuinely common home for this code and an awkward one: it turns up in a long line of Mercedes passenger diesels, in Volkswagen and Audi 2.5 TDI applications, and in mid-size vans and light trucks. On every one of them, **cylinder 5 is the last plug in the row, at the back of the engine, closest to the bulkhead** — the one where a plug that would take ten minutes at the front of the engine takes an hour because there is no straight line to it and no room to swing a wrench. If the engine is a V, cylinder 5 is often the first cylinder of the second bank, which means the fault has jumped to a side of the engine that may be entirely different to work on.
The second consequence is a parts one, and it catches people out at the counter rather than in the driveway. **Glow plugs are sold in sets of four, six and eight because that is how many cylinders engines usually have.** A five-cylinder needs an odd number, so the cheap multi-pack that looks like the obvious buy leaves you one short, and buying two four-packs to get five means paying for three plugs you will not use. If you are replacing the set — and on an engine where the rear plug is this awkward, replacing the set is a reasonable call — count first and order to the count.
There is one more thing an odd-cylinder engine changes, and it is about how the symptom presents. An inline five does not fire evenly the way a four or a six does; it has a natural rhythm of its own that is part of the reason people like the sound. That characteristic beat makes a single cold-start misfire harder to pick out by ear than it would be on a smoother engine, so the complaint often arrives as "it takes longer to start when it's cold" rather than "it runs rough on one cylinder." Do not let a lack of obvious roughness talk you out of the code. Measure the plugs.
Common causes
- Cylinder 5 glow plug element open or drifted high in resistance with age
- Corroded, heat-damaged or loose terminal on the cylinder 5 plug stud
- Branch wire to cylinder 5 chafed or broken where it runs behind the engine
- Failed cylinder 5 output channel inside the glow plug control module
- Wrong-specification plugs fitted previously — a common outcome when an odd cylinder count met a set of four
- Water or road-salt corrosion at the rearmost plug connector, which sits low and gets little airflow
- Failed glow plug relay, high-current fuse or module supply where other cylinders are reporting too
- Poor engine-to-body ground shared by the glow circuit
- Connector strip or bus bar terminal that has lost clamping tension
Symptoms
- Longer cranking than normal on a cold start, worse the colder it gets
- Rough running or a light misfire for the first minute from cold, clearing as the engine warms
- White or grey smoke on a cold start that disappears with temperature
- Check engine light with P0675 stored, sometimes alongside other cylinder glow plug codes
- A complaint that presents as slow starting rather than obvious roughness, particularly on five-cylinder engines
- Glow plug or wait-to-start indicator flashing after start on some vehicles
- Completely normal running once the engine is at operating temperature
Diagnostic steps
- 1.Identify the engine before anything else — cylinder count and configuration. P0675 cannot come from a four-cylinder, and whether cylinder 5 sits at the back of an inline engine or at the start of a second bank decides the entire approach.
- 2.Look up the manufacturer's cylinder numbering for that specific engine rather than counting from the front. On V-configuration diesels the fifth cylinder is frequently the first one on the opposite bank.
- 3.Read and record every stored code. If more than one glow plug channel is reporting, investigate what they share — module, relay, high-current fuse, supply and ground — before touching individual plugs.
- 4.Measure the resistance of every glow plug on the engine at its own terminal and compare them side by side. A healthy set reads closely matched and low; the outlier is the answer.
- 5.Inspect the cylinder 5 terminal, retaining nut and connector for corrosion and heat damage. On a rear-mounted plug this connector is the one that collects moisture and sees the least airflow.
- 6.Check continuity from the module output to the cylinder 5 terminal, paying attention to where the branch passes behind the engine or across to a second bank.
- 7.Confirm battery voltage and ground integrity under load, since the glow circuit draws heavily and a marginal supply skews every channel's reading.
- 8.Count the plugs before ordering parts. An odd-cylinder engine does not match the standard four-pack or six-pack listing.
- 9.Bring the engine to operating temperature before attempting removal, and work a stubborn plug loose in small increments rather than in one pull.
- 10.Verify the fix after a genuine overnight cold soak, because the glow circuit is only exercised during preheat.
Repair cost
$70 – $950
Diagnosis runs $80 to $180. A single glow plug with reasonable access is $120 to $380 fitted; a rear plug on an inline five or six, where the bulkhead, a heat shield or intake pipework is in the way, is commonly $300 to $700 for the same $25 part. Terminal or branch wire repair is $90 to $260. A relay or high-current fuse is $30 to $150 and is the cheap outcome when several channels report together. A glow plug control module is $250 to $750 fitted. If you are replacing the full set, budget for the actual cylinder count rather than a four-pack — five or six plugs typically adds $70 to $220 in parts over doing one, and on this engine the labour is already spent.
Estimate your repair
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Open the Repair Cost Estimator with glow plug / glow plug module replacement 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.