Toyota Wish: 1AZ-FSE Oil Pump Drive Gear and Chain Tensioner Failure

The 1AZ-FSE drives its oil pump via a short roller chain and a pressed-on drive sprocket on the crankshaft. The sprocket and chain tensioner are known to wear prematurely on higher-mileage units, producing a characteristic metallic rattling on cold start that typically diminishes as oil pressure builds but returns and worsens over time. In severe cases the tensioner loses control of chain slack entirely, causing the chain to jump or the pump to under-deliver oil; sustained low oil pressure from this mechanism has been documented as a precursor to spun main bearings and irreversible crankshaft damage, making early diagnosis critical.

• Metallic clattering from lower front of engine on cold start, lasting 5–30 seconds before partially subsiding
• Oil pressure warning lamp flickering at idle when fully warm
• Oil pressure gauge reading low at idle on instrumented vehicles
• Knocking deepening to a rod knock in advanced cases indicating bearing starvation

1. 1

   Check oil pressure with a mechanical gauge at idle — below 28 kPa at operating temperature is a red flag.

2. 2

   Inspect service history for regular oil changes; sludge from extended intervals accelerates tensioner wear.

3. 3

   If a workshop inspection is possible: Listen for metallic rattling at the front-lower engine on a cold start; use a mechanic's stethoscope to isolate from the timing chain area.

4. 4

   Remove the front cover on suspect engines to inspect sprocket teeth and tensioner blade condition.

Parts involved: Timing chain.

$1,200 to $3,500 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 oil pump chain and tensioner ever been inspected or replaced?”
• “Does it make any rattling noise for the first few seconds when you start it from cold?”
• “Can I see the full oil change service history — what intervals were the changes done at?”

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.