Glow Plug Failure
DIY-friendlyGlow plug failure is one of the most common cold-start complaints on the T1N Sprinter. When one or more plugs fail — or the glow plug module/relay loses an internal fuse — the engine becomes hard or impossible to start in cold weather.
Symptoms
- Hard or no-start condition in cold weather, especially below freezing temperatures [5, 12].
- Extended cranking time in cold weather — some owners report several minutes of cranking with only 3 working glow plugs [5].
- Check Engine Light (CEL) illuminated on cold starts, often clearing after the engine warms up or after several warm restarts [15, 16, 28].
- CEL returns on the next cold start even after clearing [28].
- Fault codes P0673 (cylinder 3 glow plug circuit), P0674 (cylinder 4 glow plug circuit), P0675 (cylinder 5 glow plug circuit), and P0380 (glow plug heater circuit A malfunction) stored in the ECM [4, 9].
- Glow plug warning light on the dash that goes out once the engine fires [0].
- "Start error" light on the dash when glow plugs are insufficient for cold cranking [5].
Causes
- Individual glow plug element failure due to age or high mileage — one owner noted a failure at 180k miles [13].
- Internal fuse blown inside the glow plug relay/module: when a glow plug fails it often blows the internal fuse for that cylinder, so replacing only the plug may not solve the problem [3].
- Glow plug tip mushrooming, often caused by using ether (starting fluid) while glow plugs are energized — ether causes the tips to deform and can make plugs impossible to remove [6].
- Glow plug threads seizing in the head due to carbon buildup, making removal very difficult especially on high-mileage engines [2, 6].
- Inadequate voltage reaching the plugs due to a weak or aging battery compounding marginal plug performance in extreme cold [3].
Diagnosis
- Scan the ECM with a capable scanner (e.g., Autel) for glow plug DTCs such as P0673, P0674, P0675, or P0380 to identify which cylinder circuit has failed [4, 8, 9].
- Note whether the CEL appears only on cold starts and clears after the engine warms — this pattern strongly suggests one or more failed plugs rather than a wiring fault [15, 16, 28].
- As a trial, put the van in a heated garage overnight and attempt a cold start in the morning; if it starts normally, the problem is temperature-related and glow plugs or the module are suspect [3].
- Cycle the glow plugs by turning the key to 'on' and waiting for the dash light to go out, repeating several times before cranking — improvement suggests marginal plugs that are still partially functional [5].
- Inspect and test the glow plug relay/module: the module contains internal fuses (one per cylinder) that blow when a plug fails; replacing only the plug without addressing a blown internal fuse will not fix the problem [3].
- Check battery voltage — a weak battery can compound hard starting when glow plugs are already marginal [3].
Repair
Replacing glow plugs on the T1N is a straightforward job that most mechanically inclined owners tackle themselves, though the 2003 and earlier models have a large intake manifold that obstructs access and makes the job more involved [6]. The primary risks are snapping a plug off in the head or stripping the threads, both of which turn a simple job into a major repair [2, 6]. Pre-soaking plugs with penetrating oil (e.g., Kroil) well in advance greatly reduces the chance of breakage [6]. In addition to the plugs themselves, the glow plug relay/module should be inspected and likely replaced, as a failed plug often blows an internal fuse inside the module [3].
Read first
- Never use ether or starting fluid while glow plugs are active — it causes the plug tips to mushroom, making them impossible to remove and potentially destroying the threads in the cylinder head [6].
- A seized or broken glow plug tip left in the head is a serious repair requiring professional extraction — if a plug will not turn freely after soaking, stop and consult a professional rather than risk snapping it off [2, 6].
Tools
- Socket set with glow plug socket (typically 10mm hex)
- Torque wrench
- Penetrating oil (e.g., Kroil)
- Mirror or inspection camera (especially useful on 2000-2003 models with large intake manifold)
- OBD2/Sprinter-capable scanner (e.g., Autel Maxi AP200) for reading and clearing DTCs [8]
Steps
- Scan the ECM and record all fault codes before beginning work, noting which cylinder circuits are flagged [4, 9].
- Allow the engine to cool completely before attempting plug removal to reduce the risk of seizing.
- Apply penetrating oil (e.g., Kroil) liberally around each glow plug and allow it to soak for several hours or overnight before attempting removal [6].
- On 2003 and earlier T1N models, note that the large intake manifold significantly obstructs access to the glow plugs — use a mirror to locate plugs and plan your approach accordingly [6].
- Remove the glow plug electrical connectors, then carefully unscrew each plug. Do not apply excessive force — if a plug does not move freely, re-apply penetrating oil and wait longer [6].
- Inspect each plug visually for a mushroomed or deformed tip; mushrooming is a sign of ether (starting fluid) use and indicates the plug has been damaged [6].
- Install new glow plugs (Bosch or Beru are recommended brands for T1N) [13]. Torque to manufacturer specification.
- Inspect the glow plug relay/module for blown internal fuses. If an internal fuse has blown, replace the entire module — a modified module with external replaceable ATC fuses is available as an alternative [3].
- Clear all fault codes with a scanner, then perform several cold-start cycles to confirm the repair and verify no codes return [4, 8].
- IMPORTANT: Never use ether (starting fluid) with glow plugs energized, as this causes tip mushrooming and can make plugs impossible to remove in the future [6].
Torque specs
- Limited corpus coverage — try the chat for diagnostic guidance.
Parts
Plain part names — affiliate links and pricing are coming in a later update.
- Glow plugs — full set of 5, Bosch or Beru brand recommended for T1N
- Glow plug relay/module — OEM replacement or modified version with external replaceable ATC fuses
Related forum threads
From the manuals
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Sources
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