Not so long ago we had to diagnose a 2010 Seat Leon 1.2 because it was running poorly at idle speed and had an engine warning light illuminated on the dashboard. The fault stored was an exhaust oxygen sensor fault, however, we also noticed the engine sounded a little noisy.

We suspected that the timing chain could be worn therefore resulting in the engine timing being out, not burning all of the fuel, causing the oxygen sensor fault and making the engine idle erratic. Testing our theory was straightforward, we screw a crankshaft timing tool into the rear of the engine block, turn the engine over until the crankshaft meets the tool, and then fit a camshaft timing tool into the rear of the cylinder head.

As suspected the camshaft tool wouldn’t fit into position due to the stretch of the chain and proving that the timing was no longer correct. A new chain, sprockets, and tensioner would be required to rectify the fault. Once the timing tools are fitted and holding the crankshaft and camshaft in the position we removed the bottom pulley, timing chain cover and sump to gain access to the chain.

Next, we removed the tensioner, chain, guides and sprockets and replaced them with new parts. The locking tools were removed so that we could rotate the engine a couple of times before making sure that we could re-fitted them easily and therefore confirm that the timing was correct. This was satisfactory so we refitted the timing chain covers and sump before replacing the oil filter and filling it with new oil.

Finally, we had to connect ODIS (Offboard diagnostic information system) to tell the vehicle that a new chain had been fitted, reset any learnt parameters and clear previous fault codes. On start-up, the engine was noticeably quieter and idling smoothly. A road test and final check ensured the oxygen sensor faults did not return and everything was working perfectly.

Car Engine timing belt