This 2018 Renault Trafic with 45,000 miles came in with hard cold starting — a classic sign of failing glow plugs on a diesel. On bench testing, one plug was completely dead and another barely glowing. All four were replaced as a full set.
Glow plugs on this 1.6 dCi engine are accessible from the top with minimal stripdown — just the coolant bottle needs moving to reach plug four. The key tool is a quarter-drive 10mm socket; a full-size drive simply won't fit.
Symptoms of Failed Glow Plugs
- Hard starting on cold mornings — especially below 5°C
- Excessive white smoke on cold startup
- Engine management or glow plug warning light
- Rough running when cold, smooths out once warm
- Longer-than-normal cranking before firing
Also Applies To — Same 1.6 dCi Engine
- Vauxhall Vivaro (older shape)
- Nissan Primastar
- Fiat Talento
Tools & Parts Needed
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Step-by-Step Guide
Disconnect All Four Glow Plug Connectors
Open the bonnet. The four glow plug connectors are small black tabs sitting on top of the engine — one per cylinder. Use long nose pliers to gently pull each one off. Plugs 1–3 are straightforward. Plug 4 is buried at the back — push the tab on the coolant bottle to release it and move it aside, then gently pull the small top coolant pipe free to create enough clearance.
Remove All Four Glow Plugs
Fit the 10mm quarter-drive socket on an extension and ratchet. Looking carefully down past each connector location you'll see the shiny glow plug hex head. Seat the socket fully, crack each plug loose, then spin out by hand. Use long nose pliers to lift each plug clear. Number 3 may be slightly tighter — persevere, it will come.
Test the Old Plugs
Connect a jump pack earth to the body of each plug and briefly touch positive to the tip. A healthy plug glows bright red within 1–2 seconds. On this Trafic: plug 2 was completely dead, plug 3 was barely glowing and nearly gone, plugs 1 and 4 were working. All four replaced as a service item regardless.
Fit the New Glow Plugs
Apply a tiny amount of copper slip to the threads of each new plug — this prevents future seizure. Drop each plug into its hole, let it find its seat, then use the 10mm socket to wind it in by hand first to guarantee no cross-threading. Tighten to a firm nip only — do not overtighten.
Refit Connectors & Test
Press each connector back onto its glow plug until you feel a click. Plugs 3 and 4 can be fiddly — use long nose pliers gripping where the cable meets the plastic and press firmly. Refit the coolant bottle and pipe, making sure the pipe clips in fully on both sides. Start the engine — it should fire readily with no warning lights showing.
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