P0670 Land Rover — Glow Plug Control Module Circuit: Causes & Fix Cost

P0670 means the ECU has detected an electrical fault in the glow plug control module circuit. On Land Rover diesels — especially the 204DTD Ingenium and 306DT V6 — this is usually a fuse, relay, or wiring issue, not a failed module. Diagnose cheapest-first to avoid unnecessary replacement.

Most common real cause: a blown fuse or faulty relay — typically £50–£150 fitted [PATTERN DATA]
Worst case: failed glow plug control module, £300–£800 fitted [PATTERN DATA]
Commonly seen alongside glow plug warning light and white smoke on cold start
Often appears with P0671 or P0672 — the combination points to individual glow plug circuit faults

Do not let anyone sell you a new glow plug module before the fuses, relays, and wiring have been checked. Full diagnostic order below.

What P0670 Actually Means

The glow plug control module (also called the glow plug relay or timer) is responsible for supplying power to the glow plugs during cold start, and sometimes for post-heating after start to reduce emissions. The ECU monitors the module's circuit for electrical integrity — voltage, current, and continuity. P0670 is logged when the ECU detects a circuit fault in the module's control circuit — typically a short to ground, an open circuit, or an excessive current draw. Crucially, this code describes a circuit problem, not a component failure. The module itself could be faulty, but equally the issue could be a blown fuse, a failed relay, corroded wiring, or a poor earth connection. This distinction is the difference between a £50 fuse and a £500 module replacement. This code appears across the full range of JLR diesel engines, from the 204DTD Ingenium to the 306DT V6, and the diagnostic approach is essentially identical regardless of which engine triggers it.

Symptoms You'll Notice Alongside It

Engine management light illuminated, usually amber
Glow plug warning light flashing or staying on
Hard starting when the engine is cold — extended cranking, especially in winter
Rough idle or misfire immediately after a cold start — see misfire and rough idle
White smoke from the exhaust on startup (unburned diesel)
Increased emissions and potential limp mode in some models

Common Causes, Ranked

Ordered by how often each turns out to be the real culprit — with typical fitted cost against each, so you can sanity-check any quote you've been given.

Cause	Likelihood	Typical Cost (fitted)	Notes
Blown fuse or faulty relay	Very High	£50–£150	Cheapest fix — check the glow plug fuse and relay first
Wiring issue (corrosion, broken wire, poor earth)	High	£120–£300	Common on older vehicles; often intermittent
Faulty glow plug control module	Medium	£300–£600	Module internal failure — not always the cause
Short circuit in glow plug harness	Medium	£150–£400	Wiring chafing against engine or chassis
ECU software or internal fault	Low	£200–£800	Rare — only if all other checks are clear

Cost figures [PATTERN DATA] — indicative independent-specialist pricing, not drawn from our engine replacement dataset.

Diagnostic Order — Cheapest First

Check fuses and relays

Locate the glow plug fuse and relay in the fuse box (often under the bonnet). Replace any blown fuses or suspect relays. This is the cheapest and quickest fix.

Inspect wiring and connectors

Visually inspect the wiring to the glow plug module and each glow plug for chafing, corrosion, or broken wires. Check earth points for cleanliness and tightness.

Test the glow plug module with a multimeter

A specialist can check for 12V supply, ground, and control signal from the ECU. If all are present and the module doesn't power the glow plugs, the module is faulty.

Check individual glow plug resistances

A shorted glow plug can overload the module and cause circuit faults. Measure each glow plug's resistance; replace any that are out of spec.

Only then consider module or ECU replacement

If all above check out and the fault persists, the module itself may be faulty, or in rare cases, the ECU has an internal driver issue.

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Not sure where to start?

Our diagnostic wizard walks the same order, or confirm your engine first with the registration lookup.

Can You Still Drive It?

Yes, but with limitations. P0670 is not an immediate engine-destroying fault. The vehicle will still start and run, especially in warmer weather. However, in cold conditions, the engine may be difficult to start, and you may experience rough running or white smoke until the engine warms up. Prolonged driving with faulty glow plugs can cause increased emissions, poor fuel economy, and potential DPF issues (on diesels). It's safe to drive to a garage, but avoid leaving the car parked in freezing conditions for long periods if you need a reliable start. Get it diagnosed within a week or two.

Related Fault Codes

P0670 often appears with other glow plug codes. The combination can pinpoint the specific issue.

P0671 — Cylinder 1 Glow Plug Circuit

Points to a specific glow plug or its wiring — often a bad plug or connector.

P0672 — Cylinder 2 Glow Plug Circuit

Similar to P0671 but for Cylinder 2.

P0673 — Cylinder 3 Glow Plug Circuit

If multiple cylinder codes appear, suspect a wiring harness or module issue.

P0674 — Cylinder 4 Glow Plug Circuit

Indicates a fault on Cylinder 4 — check the plug and wiring.

Timing Chain Diagnosis Guide

While not directly related, rough starting can sometimes be misdiagnosed — this guide helps distinguish.

Frequently Asked Questions

Can I drive with P0670 on a Land Rover?

Yes, for short periods — but cold starts will be difficult, and you may notice rough running and white smoke. It's safe to drive to a garage, but avoid relying on the vehicle in freezing temperatures without getting it fixed.

Does P0670 always mean the glow plug module has failed?

No. In most cases, a blown fuse, faulty relay, or wiring issue is the culprit. The module itself is less common to fail. Always check the simple things first.

Will clearing the code fix it?

Only temporarily. The code will return as soon as the ECU detects the circuit fault again, usually on the next cold start or after a few drive cycles. Clearing it without fixing the root cause just masks the problem.

How much should diagnosis cost?

Expect one hour of diagnostic time at an independent JLR specialist — around £60–£100. Many will offset this against the repair if you proceed.

Can a bad glow plug cause P0670?

Yes, a shorted glow plug can overload the module and trigger a circuit fault. Checking individual glow plug resistances is part of a thorough diagnosis.

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Cheapest-First AlwaysWe rank causes by likelihood and cost, not by what's profitable to quote.

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Honest About CostWhere a fault is usually cheap to fix, we say so plainly.

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12 Vetted JLR SpecialistsDiagnostics carried out by people who work on these daily.

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