🚗 Classic Fault — Mercedes-Benz (1976–1985)
W123 240D glow plug failure
💰 Estimated Repair Cost
$5 – $40 GBP
Parts and labour estimate
🔧 Tools Required
Multimeter, glow plug socket
📋 Overview
Diesel W123s depend on glow plugs for cold starting. Individual plugs fail without warning, causing hard starts.
🩺 Symptoms
- Hard cold start — engine cranks many times before firing
- white smoke on cold start
- misfiring when cold
🔍 Possible Causes
- Failed glow plugs (one or more)
- failed glow plug relay
- flat battery unable to crank fast enough
🛠️ Diagnosis Steps
Test each glow plug with multimeter — should read 0.5-2 ohms. Test relay output voltage when energised
✅ Most Confirmed Fix
Glow plug replacement — replace all at once
93% of users confirm this fix worked (48 reports)
🩺 Related Symptoms
🔗 Other Mercedes-Benz Faults
Own a Mercedes-Benz ?
Share your experience with this fault — or report a different issue. Your knowledge helps other classic car owners worldwide.