2003 Prius P3191 and P3101: Fix

My parents' Gen 1 2003 Prius, at 99,030 miles, wouldn't start, and I thought I'd share the problem description and the fix that worked for me, for others who see the same symptoms.

My Mom called, saying the car wouldn't start. I first noticed that the dome light seemed quite dim. I tested the 12V battery, and it was at 9V (and 8 years old). I replaced it with a NAPA Optima BAT N9951RYEL (the conversion from "pencil-post" to standard terminals had already been done). I did have to re-bend the battery tray to fit the new battery length.

The car then would "start", and run for about 8 seconds, and then the engine would die with pretty bad knocking, and the check engine light would come on. I soon learned (from PriusChat postings), that the engine had never really started, and that MG1 was simply driving it for the entire time. I re-tried this 4 times, and then stopped, concerned for the SOC (State of Charge) on the HV battery.

I pulled up the DTCs from the ECM and the HV ECU, and found P3191 and P3101 (inf 205). P3191 is 'engine "dose" not start'. Given that the car is at 100K miles, I bought a new set of NGK Laser Iridium spark plugs ("cause, lasers, right?"). I also picked up some MAF cleaner, throttle plate cleaner, and starter fluid.

I pulled off the air filter box, and inspected the MAF sensor, which was evenly coated with a layer of blackened dust. A quick spray of MAF cleaner restored it to a shiny state.

Next, I cleaned the throttle plate pivot points. The throttle plate didn't look too bad. I did note a slight amount of clean engine oil at the bottom of the intake manifold, but it's hard to see how this would be pulled into the cylinders. I didn't have a chance to clean it out, but I think with the right custom tool it should be possible to soak it up with a shop paper towel through the throttle body opening. This is supposed be due to engine oil overfilling, but the car last had an oil change 6 months ago, and has been running fine since then.

Finally, I replaced the spark plugs, which didn't look all that bad for 100K miles, but definitely needed replacement.

Even though the SOC from the HV ECU was reading 10.5%, which I was sure meant that MG1 wouldn't be able to turn over the engine, I sprayed one short burst of starter fluid in, started the car, and bingo! It started and ran with no check engine light. The starter fluid probably wasn't necessary at all. Very shortly afterwards, the SOC was reading 58%. I wonder if SOC is not very reliable until the HV ECU and the HV Battery ECU have seen energy flow into or out of the battery.

I really think the MAF sensor was the primary problem, but I can't be sure.

Also, one other note: with a Tactrix Openport 2.0 connected to the OBD port, shifting the car into "D" while running, with the driver's door open, causes the red triangle of death, and a constant beep. Shifting out of "D" causes both the beep and the red triangle of death to disappear. Very weird. This must be a safety feature: if a technician is connected to the OBD port, and puts the car in drive with door open, he must need a special warning! There is actually an internal dummy DTC created in the ABS ECU to support this mode: when the driver's door is closed, the DTC spontaneously disappears, which should never happen. Unplugging the Tactrix made this condition disappear.

The HV battery cells all look closely matched in voltage, so I'm hoping that my parents can get a few more years out of it.

 

Thanks for the info on the oil in the intake manifold. The car has had the engine oil changed regularly, but not much else. I'm planning on changing the transaxle fluid (Toyota OEM) and the interior and engine filters. The coolant is original, rated for 120K miles, but it has been 13 years. The brake pads and disks look great. Anything else I should consider?

 

Yes, this stuff has been around forever. It's basically ether. I just sprayed a short burst down into the throttle body before starting the engine.

I don't think this was necessary, but I was very concerned about the traction battery SOC, and how many more cranking attempts were left.

This can help to show whether there is a fuel delivery problem, but will only keep the engine running for a few seconds. You don't want to spray too much of it, as it strips the oil off the cylinder walls if used to keep an engine running.

Have you checked the MAF sensor? I think this was the root cause of my problem.