How to Inspect & Replace the Drive Belt
2004-2009 Toyota Prius


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This is a pretty simple job that doesn't require many tools. It can be accomplished without removing the lower right engine cover assuming you don't have huge arms. Getting the new belt in around the crankshaft wheel is a very tight squeeze but I was able to get it to work. This tutorial assumes you are not removing the lower right engine cover. If you want more room to work put the car on ramps and remove the lower cover below the belt. This belt should be replaced at 100,000 miles and inspected at least yearly. However, it's easy to quickly check it when you open the hood. Doing this job yourself should easily save you $100!

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Tools Needed:

Parts/Supplies Needed:

1) Optional: Remove the front engine bay cover if you want a little extra room to work.

2) Use a 10mm socket to loosen the air cleaner inlet hose clamp.

3) Pull the inlet hose off and set it out of the way.

Overview: Inspect the belt for cracks on the ribbed side that goes over the water pump wheel (below the tensioner pulley). The belt should be replaced if you have more than 7 cracks per inch on the interior. Also if the exterior of the belt looks glossy that could indicate it has been slipping and is loose. The 14mm nut highlighted in green is for the tensioner pulley, the 12mm bolt circled in red is what adjusts the tension on the belt. In order to remove the belt or adjust tension you first loosen the nut enough so the pulley can travel up or down the track behind it. The tensioner bolt is then used to loosen or tighten the drive belt.

4) Use a 14mm 6-point socket to loosen the pulley tensioner nut. Do NOT fully remove it, just loosen it a few turns. It will probably be on way too tight. I was unable to loosen it using my 3/8" socket and my normal breaker bar wouldn't fit in the space. So I went to the home store and picked up a 3/4" x 24" piece of black pipe for ~$8. This fit over my 3/8" socket nicely and I was then able to easily loosen the nut with the extra leverage.

5) Use a 12mm socket with an extension to loosen the tensioner bolt. The more you loosen it the more the pulley will slide down the track. Loosen this enough to get the old belt off but you don't want it to come out completely. You can check the back of the tensioner track to gauge. You can loosen the 14mm pulley nut more to gain the clearance you need to remove the belt. Once the belt is out turn the water pump wheel to make sure its moving easily.

Old belt which I'm pretty sure was never replaced...that's 148,500 miles! Obviously a ton of cracking but it was still going.

New drive belt

6) Install the new drive belt. Fit the belt around the crankshaft pulley first. I was able to just barely get my arm way down there to make sure the belt was centered over the wheel. Once that was seated I kept tension on it and brought it over the tensioner pulley, then over the water pump wheel. Tighten the 12mm tensioner bolt enough so the belt won't fall off. Tighten the 14mm nut enough so the pulley can still slide up the track but isn't super loose.

7) Adjust the drive belt tension. This is where the average do-it-yourselfer won't have the proper tools. The belt tension should be checked on the longest run of the belt which is between the crankshaft pulley and tensioner pulley. I found a nice video on how to estimate the proper tension below. Basically twist the belt in the middle of the longest run, it should twist 90 degrees but no more. If you can't easily twist the belt past 90 degrees you have proper tension. If you can't twist to 90 degrees the belt is on too tight.


8) Tighten the 14mm pulley bolt and torque to 30 ft-lb (40 Nm, 408 kgf-cm).

9) Connect the air inlet hose and torque the 10mm nut to 27 in-lb (3 Nm, 31 kgf-cm).

10) Start the car and check that everything is running properly, run the engine for 5 minutes then shut the car off.

11) Re-check belt tension. The repair manual says that when applying 22 ft-lbs of pressure on the belt between the crankshaft pulley and idler pulley it should deflect 11-15mm (0.43" - 0.59"). I just did the 90 degree twist check. If the belt has become too loose, loosen the 14mm nut, tighten the 12mm tensioner bolt as needed then torque the 14mm nut down when you have proper tension.





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Last revised: Sunday, 29-Oct-2023 16:36:54 EDT