Mercedes-Benz GLA: OM651 2.1CDi Timing Chain and Guide Failure

The 2.1-litre OM651 diesel engine in GLA 220d models mounts its timing chain at the rear of the block, driven by a hydraulic tensioner and guided by nylon-composite plastic rails. Heat cycling and oil starvation cause the plastic guides to crack and crumble progressively. The tensioner design lacks sufficient oil pressure reserve during cold starts, allowing chain slack to develop before full oil pressure is achieved. Chain elongation can cause the chain to jump teeth on the camshaft sprockets, producing immediate risk of valve-to-piston contact and catastrophic internal damage. Pre-2014 engines carry the highest risk; updated tensioner components were introduced from approximately 2014 but do not eliminate the failure mode entirely.

• Metallic rattling or chattering from the rear of the engine on cold start, settling after warm-up
• Check engine light with camshaft position or timing correlation codes P0016 or P0017
• Rough running or hunting idle immediately after cold start
• Plastic guide debris visible in engine oil during drain at service

Cold-start the engine and stand at the firewall side listening for a sustained metallic rattle from the rear of the engine lasting more than two to three seconds. Request full oil service history confirming intervals not exceeding 15,000 km. Connect STAR diagnostics and check for stored or pending camshaft correlation codes P0016 and P0017. On any vehicle above 100,000 km with no documented timing chain work, budget for preventive replacement before purchase.

Parts involved: Timing chain.

$3,500 to $8,000 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the timing chain, tensioner, or plastic guides ever been inspected or replaced?”
• “Is there a full oil service history confirming regular changes at or below 15,000 km intervals?”
• “Has any rattling noise ever been noticed from the engine during cold starts?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.