Main engine ECU requires replacing

I've attached the relevant TSB that relates to your issue. There is nothing "faulty" with the engine ECU in your car. However, the latest version ECU allows more time for the engine to start before logging a diagnostic trouble code. Note that the current part number of that ECU is 89661-47054 (see the top of page 2 of the TSB.)

On US vehicles, the engine ECU is located behind the glovebox to the right of the cabin air filter. If you can access this part, perhaps you can find the part number label and see how downlevel your engine ECU is.


If your engine is tuned-up, it may start faster so that the engine ECU will not log a fault code. I suggest that you consider the following:

• clean the throttle body interior and throttle plate, as dark gunk tends to accumulate on those parts. This is because the Prius engine uses the Atkinson cycle which allows the intake valves to remain open as the engine crankshaft moves up from bottom dead center. Hence some exhaust gases can enter the intake manifold and condense on the throttle body.
• replace the iridium spark plugs, using only the correct replacement plugs (the service interval is 60K miles)
• replace the engine air filter if dirty
• ensure that the engine oil viscosity is only 5W-30 and that the oil level does not exceed the top dimple on the dipstick; have the oil changed if in doubt

If you have a recurrence of this problem, it will most likely happen in the winter when ambient temps are quite cold and the car has more trouble starting.

Good luck.

 

Great reply by Patrick, should be read by all new to the world of 2001-2003 Prius.

Only thing to add is the possiblity that a suitable ECU might be obtainable from a salvage vehicle dismantler.

 

Greetings, All!

I bought a 2001 Prius, and it's been great, no major repairs, only replacing the little battery in the trunk. But yesterday after a 2 hour drive at fast freeway speeds during a hot day, I stopped the car for an hour and when I came back and started it, it didn't start and then the engine check and triangle with exclamation point came on.

My dealer has serviced the car since new, and says I need a new engine ECU and Circuit Opening Relay. I haven't authorized the repairs yet, as the cost is about $1,500.

I started researching on line and found this incredible forum, and learned the warranty was 80,000 for the ECU. The car has 81,825 miles, so I called the dealer back and asked if they could get it covered under warranty, and they said they already thought of that and the service manager said no. Should I push it with the service manager?

I bought another 2008 Prius from the same dealer for my wife last year, and I was about to try to order 2 new 2010 plug-in Priuses from them.

The engine ECU part is most of the cost, and I feel like they should try to get it covered under the warranty. I read the TSB that was posted above, but I don't really understand it.

Thank you in advance for your opinions and suggestions!!

 

Hi Robert,


It would not hurt for you to ask the dealer's service manager about this, then escalate to the Toyota Customer Experience center if necessary. If that fails, then I suggest you make sure the basics are taken care of:

• replace the iridium spark plugs and engine air filter
• clean the throttle body and throttle plate
• make sure the engine oil is 5W-30 viscosity and not overfilled.

The TSB is basically saying that, after ruling out the basic issues listed above, there are two possible reasons for the no-start condition. One is insufficient fuel line pressure. This is the reason that the fuel tank and the circuit opening relay are listed as items to check.

The other reason is that the engine ECU does not allow enough time for the engine to start before logging DTC P3191, which is the engine no-start fault code. The current revision ECU allows more time for the engine to start. However, since you've owned the car from new and only now are faced with the problem, it is possible that if you do an engine tune-up (the basics listed above), then the car may work well for you again.

 

Hi Patrick,

Thank you so much for taking the time to respond!!

Curiously, I had a major service 1,000 miles ago, at 80,000 miles, and that included replacing the plugs and the engine air filter. It was the first time the plugs had been replaced since I owned the car. I don't know if they cleaned the throttle body and throttle plate, and I'll ask tomorrow. I had Mobil 1 fully synthetic put in before I drove it off the lot, and only use that for oil changes. I think the viscosity is 5W-30. I assume they did a tune up when they did the major service.

Because I just had the major service, I was wondering if that contributed/caused the problem, but from what you're saying, I guess the opposite is true.

This afternoon I spoke with my usual service writer and found out that the service writer who helped me early this morning never asked the service manager to call Toyota to try to get authorization for the repair to be covered by the warranty. That was troubling, and they have promised to do that in the morning.

What I still don't understand is whether the replacement of both the engine ECU and the circuit opening relay are needed. From the TSB and what you're saying, I gather that the ECU detected that the engine didn't start up right away, so the problem is not the ECU, since the ECU is only a detector of the problem. Am I misunderstanding things? Should they first replace the circuit opening relay to see if that alone solves the problem?

Sorry if I'm a bit dense, but this is all new to me!

Patrick, I really appreciate your time and expertise in guiding me through this!!!

Robert

 

Hi Robert,

Yes, since the circuit opening relay (aka fuel pump relay) costs around $75, it would make sense to replace that first and see if that solves the problem. This relay lives in the relay/fuse box next to the inverter, and you can change it yourself if you want to save the labor charge.

If you have access to a digital multimeter, you can test the relay before replacing it. To do so, remove the relay/fuse box cover and look at the map on the underside of the cover to find the circuit opening relay. Gently pry the relay out of its socket using a small flat-blade screwdriver.

The relay has four terminals, two for the relay coil and two for the switched contacts. The relay coil terminals will show ~100 ohms resistance or so. The other terminals will show infinite resistance. Apply 12VDC to the relay coil terminals and measure the resistance across the switched terminals. If more than 0.5 ohm (after accounting for the resistance of the multimeter test leads), then replace the relay.

You are correct that the engine ECU is merely reporting that the engine is slow to start. If you can remove the glove compartment (same as when changing the cabin air filter) then you may be able to find the part number label on the engine ECU. If so, then you can compare to the part numbers shown on the TSB.

The current revision ECU will allow more time for the engine to start before logging an error code, which is basically covering up the basic problem of engine slow start. However, the slow start may be due to mechanical wear resulting from age (low cylinder compression for example). If the car does not display other driveability symptoms, then it is not helpful for the error code to be logged.

 

Thank you, Patrick!! So far the manufacturer's regional representative has agreed to cover 50% of the ECU part. I think this is unfair and insufficient due to the TSB you brought to my attention on the identical parts, and due to the 1,000 mile difference between the 80,000 mile warranty and my actual mileage. I am hoping that the manufacturer will agree with me. They are going to let me know tomorrow.

Thank you again!!
Robert