Intermittent Starting - Gen 1 '01 Prius

Welcome to the club!

Problem starting often (not aways) is associated with a sticky throttle plate:
Cleaning Prius Throttle

However, the ambiguity group also includes dirty MAF sensor and others. I'd recommend scanning many of the past threads and think about where you want to go with the car.

First car?

Bob Wilson

 

MAF filter?

 

It is how the MAF gets dirty. <grins>

Meant MAF sensor, not filter. Corrected the original post, thanks.

Bob Wilson

 

"you can turn the key, but the system turns off all the electrical until you stop trying to start." Hi there and welcome to PC!
As Bob stated above the throttle body area is prime suspect here and you should check that out, but this sure sounds like a low 12v battery. You can check it with a voltmeter while the car is off, just measure right across the battery (inside leftside trunk area). If it's below 12vdc then it needs to be replaced. You see the car needs the 12v battery to "boot up" all the computers and to start the engine, after the engine starts the inverter takes over all 12v power and even charges the 12v battery back, not to mention also charges the HV traction battery as well. One other easy test would be to check the voltage across the 12v battery while the car is on(ready), and now the voltage should be around 13.8V (charge voltage from inverter). But you said that once started it runs good so I'm betting it will be easy to fix. Good Luck!

 

The "ambiguity group" means the potential causes of a problem. Which one(s) is ambiguous until diagnosis and corrective action makes the symptom go away. For example, 'w2co' pointed out a weak 12 V battery could also cause a similar symptom and needs to be checked.

You may want to look for a set of shop repair manuals, 2001-03:

• Volume 1 - covers diagnosis
• Volume 2 - covers repair actions

These are available on Ebay from time to time and run about $100-200 for the set. They are your roadmap to understanding the car. If you have a 'do it yourself' bend, start with these.

Are you close to "Arts Automotive" or "Lucious Garage?" They are well known Prius shops and good places to have a difficult car looked at. Of course there are the local Toyota shops.

Bob Wilson

 

Please take a good look at the three icons on the MFD. One of the three should be lit up. My guess is that the lit icon will be the car symbol w/ !, which is the hybrid system warning icon.

Besides the warning icon appearing in the MFD, are any other warning lights on (for example, the red master warning triangle light, check engine light, ABS or brake warning lights, etc.?

Pls do not underestimate the ability of a marginal 12V battery to make trouble and cause weird problems to happen. If the battery is more than four years old, I'd suggest replacing it to rule that out as an issue.

If you are able to successfully start the car in 1 out of 3 attempts, the car performs normally, and no warning lights remain on, perhaps the ignition switch needs to be replaced.

If you should find that the problem is more deeply rooted than a bad battery or ignition switch: since generic OBD-II code readers probably won't be able to retrieve diagnostic trouble codes logged by the hybrid vehicle or traction battery ECUs, you'll need to take your car to your local Toyota dealer so that the DTC can be retrieved and a diagnosis provided to you. You'll probably be charged for a couple of labor hours, for this service.

 

So the problem starting happens just when the car is cold? If you go somewhere and the car is hot, does it start while still warm?

"PS" - power steering, "battery" large group, "Car symbol with exclamation over it" master alarm.

The car has the ability to flash, two-digit error codes by putting a jumper in the OBD connector found under the dash to the left of the steering column:

If you run a jumper from pin 13, Tc, to pin-4, chassis ground, and turn the car on, it should trigger the connected ECUs to flash any two-digit codes stored in the control units. This may not lead to a diagnosis as many interesting codes have no two-digit equivalent. Still, it is built-in.

If you are on a tight budget, you may be able to get a free code reading from some of the auto parts stores. However, you can also get a code reading from the local Toyota service center, for ~$100.

I've tested several over the counter code readers and they are a pretty poor lot with limited code reading capability and some have problems connecting to the NHW11.

The Auto Enginuity is usable but at $300, pricy. Still, it is the best of a bad lot. Check out the threads discussing what works and doesn't work. If configured using ISO 9141 and KWP2000, it is usable but the adapter documented in this tread seems to be a better solution.

I can rent a Graham miniscanner but instrument deposit is steep and it is limited to HV, Engine, and Battery ECU codes. Compared to the Auto Enginuity, it is plug-and-play but they are no longer made. I'm running a 'lending library' for those rebuilding their NHW11.

For somewhere between $1,200-1,500, you can get the Toyota scanner 'lite' but now you're getting into some serious money.

 

Interesting. Fortunately, the brake system has a high ratio of two-digit codes. The jumper may give a clue but now I'm wondering if the brake switch might be defective.

The car has to have the brake depressed to start. If the brake switch is defective or marginal, this might explain the intermittent starting problem. <hummmmm> It might make sense to see if something illuminated by the brake light shows the brakes actually going on when you got to start. If the brakes don't light and the car does not start and then the brakes light and the car starts . . .

BTW, if you do decide to buy an over the counter scanner, make sure it has ISO 9141 and KWP2000 capability. I can not recommend them from my testing but sometimes even a bad tool is better than no tool at all.

Bob Wilson

 

No, it doesn't.

 

Your right.

I made a quick move with the cell phone but it was too grainy. I'll do it again closer up and go over the lights and start-up sequence.

Bob Wilson

 

i would suggest checking the fuses both underhood and inside the car. Its possible that something could be wrong with one of these fuses, but do you know which of the three on the MFD is red? PS , (!) or MAIN+-??

Also it woudl help if you can get codes pulled, but since you dont want to risk driving it i woudl suggest checking the 12 volt battery and also check to make sure the engine is getting fuel, its possible you have a weak fuel pump as well.\

 

Here I am in November of 2021 with a 2002 Prius that is intermittently engaging the relay necessary to turn on the HV and start the engine. I have gone through all the other problems of an aging Gen-1 Prius with 216K miles on it.
1. Triangle of death so:

a). Bought a VeePeak OBDCheck VP11 from eBay.
b). Installed Dr. Prius app on my Android phone to identify which of the 19 pairs needed replacing.
c). Watched Youtube DIY videos for taking the hybrid battery out to get to the batteries to replace.
d). Cleaned the copper battery bus bar links with the vinegar and salt solution technique to remove the blue corrosion.
e). My Hybrid Battery Control Module (89890-47060) had also gone bad and melted the wiring together where it plugs in. Replaced the bad control module and melted wiring harness.
f). Replaced the 12V auxiliary battery with a Maxx-51r battery from Walmart.​

After all that and everything looked good and it started up no problem. I did have to use my other OBD device that reads out the error codes (as the VeePeak + Dr. Prius app doesn't do this) so that I could reset the computer to clear the traingle of death from the main display. Otherwise it was still showing a battery error even though I had replaced the bad battery modules.

Then the next morning it wouldn't start. Great... now what? Plugged in my VeePeak and ran the Dr. Prius app to check the 19 battery pairs. Oops, it says another pair are too low of voltage. After another pull out of the hybrid battery and replacement of the 2 batteries and re-assemble all is good. Or so I thought. Drove it a few days and sitting overnight it wouldn't start again. ARGH!!! Now what's wrong. No error codes to deal with yet no start. Put my charger on the 12V battery for an hour to top it off. Still won't start. Have I got a bad ignition? After a half-dozen times removing the key, inserting it the other way round, it finally started and all was normal on the displays. Shut it off, pulled out the key, and restarted another 6 times to be sure. Started every time. Fantastic, put everything back in and I'm done. But the next morning it failed to start... sigh!

An old Prius may have a faulting connector somewhere. I did the simple checks including loosening and inspecting the 12V battery lead where it bolts to the frame for rust, none found so no high resistance. In the ON key position everything works as normal, no slow power windows, lights are normal brightness, etc. So what the h... is faulting. In all my work I neglected a very simple but critical battery. The little tiny 1632 button battery that sits inside my simple key and the 2016 button battery in my key with the remote door lock/unlock and trunk unlock control. Pulled out both batteries and measured their voltage. 2.95 on 1 and 2.94 on the other (should be 3 volts). A quick trip to my local Walgreens for these batteries, plugged in the 1632, and the car started immediately and every time. Let it sit awhile and it still starts every time. The simple anti-theft mechanism wasn't detecting the proper code so it kept the hybrid battery relays from engaging to send the high voltage to the engine to start it. Simple as that once I had fixed my other major problems.

So in fixing the hybrid battery, make sure you also pull out the tiny key batteries and check their voltage. If it's more than a few hundreds of a volt below 3.0 volts that could be why your Prius won't start every time.

Final Note
When you turn the ignition key to the on position you should here 2 clicks from the hybrid battery relays (not exactly sure if 2 are turning on or one is going on and then off). When you turn the key to start your Prius you should hear 1 click from up front and 3 more clicks from the hybrid battery relays (at least that's what I hear when the engine starts up normally in my '02 Prius). If you hear no click up front then the hybrid relays aren't turning on to send the high voltage to the starter. The failure to detect the proper anti-theft code from my key because of a too low button battery voltage was preventing the proper relays from engaging to active the hybrid battery high voltage. Amazing how a simple thing like that being overlooked can prevent normal starting.