Generation 1 Prius Discussion

2003 Rough Misfire, P0303/4

invalid@example.com (Bill Cossaboom) — Fri, 08 May 2026 22:54:30 +0000

Hi. Need help on a misfire. 2003, 136k miles, original battery. Getting a rough misfiring on a warm engine. P0304 and P0303, kinda alternates between the two, 04 recorded then 03 live, then back. New-ish (<10k, OEM) coils, plugs. Swapping doesn't show anything. Compression test fine. No signs or smells, etc of coolant leaks. Never need to add any fluids. MAF/throttle body done a couple years ago. Techron run through 6 months ago. I've had it for about 4 years. I know the original owners so...

2003 Rough Misfire, P0303/4

Dr. Prius app problem in Prius Gen1

invalid@example.com (MArcin91t) — Fri, 08 May 2026 19:03:19 +0000

I'm asking out of curiosity. After the March update of the Dr. Prius app, it stopped connecting to my NHW11. Do you happen to have a similar problem? I've tried both the cheap Vbox OBD2 reader and the more expensive Veepeak, and the same problem persists.

Rattling noise - throw me a guess

invalid@example.com (ronlewis) — Mon, 04 May 2026 10:00:50 +0000

This should be a short list of possible problems. I don't hear well but a rattling noise coming from the front of the car. My guess about any car would be a bad pulley, maybe a tensioner pulley, or one on a pump or compressor. It doesn't rattle all the time, but seems to be associated with the decreasing/slack engine RPMs.

Maybe the cooling fans have a bearing that goes out? I thought about a wheel bearing, but it does it when I first start the car, before backing out.

I'll go look...

Rattling noise - throw me a guess

Daytime running lights

invalid@example.com (MArcin91t) — Sun, 03 May 2026 18:12:01 +0000

Today I decided to install a daytime running lights module that activates the high beam headlights at about 30-40% power. Unfortunately, in my country, there's a law requiring the use of headlights (low beam or daytime running lights) even during the day, which is annoying in the case of the Gen1 because it significantly dims the speedometer. I can brighten it with the button under the LCD display (where the US versions have the mph to kph button), but it still doesn't fully brighten the...

Daytime running lights

Unexplained brake noises

invalid@example.com (Iris_TheRainbow) — Thu, 30 Apr 2026 14:28:45 +0000

My 03's brakes have recently developed a noise on the front passenger side that I've not been able to explain so far

When I'm driving normally, It makes a squeaking noise that happens once per wheel rotation. When I hit the brakes, there's a single loud squeaking noise when I hit the brakes hard enough to come to a full stop.

I know its brakes because the bearing is fine, no slop, consistent force needed to spin the wheel.

I'm planning to pull the brakes off when I replace the front...

Unexplained brake noises

Can I replace 1st generation battery cells with 2nd generation battery cells?

invalid@example.com (Oregon Mom) — Wed, 29 Apr 2026 12:35:53 +0000

Can I replace 1st generation battery cells with 2nd generation battery cells?

I assuming you shouldn't mix the different generation cells in one box, but I'd like to replace ALL of the cells in my generation 1 box with all generation 2 cells.

They are the same size and have the same connections, so I hoping this will work, but I don't want to assume and then have a DISASTER!

We have our battery box open, so I'm anxiously awaiting your...

Can I replace 1st generation battery cells with 2nd generation battery cells?

Just to confirm

invalid@example.com (ronlewis) — Tue, 21 Apr 2026 15:21:34 +0000

Is there any way to confirm whether an HV battery is good in a no-start Gen1? A G1 has shown up in the local pick-u-part. It doesn't appear to have any issues except a missing cat. Of course, it almost certainly won't turn on, probably doesn't even have the key.

Any way to confirm short of removing and checking voltage on every module? Seems like I've asked this before, but forget the answers, or whether I even got any.

2003 leaves stuck in blower motor

invalid@example.com (Iris_TheRainbow) — Sun, 19 Apr 2026 23:38:24 +0000

I replaced the cabin air filter on my 2003 the other day, I bought it after it had been rarely driven for serveral years so it had plenty of time for stuff to build up and get sucked in the few times it had been driven. The air filter was black and the were so many leaves and oak seeds that were stuck in it, I was amazed that I had any air at all coming from it. However, when I removed the air filter, some of those leaves fell down onto the fan and it makes this awful noise.

I was...

2003 leaves stuck in blower motor

any links to a vid showing how to replace the fusible link?

invalid@example.com (ronlewis) — Tue, 14 Apr 2026 01:59:55 +0000

My buyer reversed the polarity while jumping and blew the fusible link inside the engine compartment fuse box. I've replace that fuse several times on other cars, and it's a PITA. Hoping to find a vid that shows how to do it, but didn't see any with a quick Google. As usual, you can find Gen2 vids on this, but not Gen1, and it's a different set-up.

Fault codes P3011, P3014, P3023...

invalid@example.com (War_Destroyer) — Mon, 13 Apr 2026 19:58:07 +0000

So my little brother has been daily driving our 2002 Prius, and told me that the car all of a sudden became very sluggish, enough that he had to use the hazard lights at every stop due to lack of acceleration. He said that both the instrument cluster and display began to flicker, that the engine became much louder even at idle, that the AC or fan blower quieted, and that a rear blower, I'm assuming the hybrid battery blower, became louder or more apparent.

I only have your basic OBD2...

Fault codes P3011, P3014, P3023...

2003 Prius with P3191

invalid@example.com (Iris_TheRainbow) — Wed, 08 Apr 2026 13:23:58 +0000

Hello!

I just bought a Gen 1 Prius because it had a battery that was less than 2 years old for basically nothing, drove it home 140 miles just fine, besides partway home the display started flashing white when I took a break, but that went away after a bit of driving. It needed some stuff done, nothing outside the realm of what I was capable of, (tires, a new hood and bumper, probably a bearing, its got some rust, including a small exhaust leak).

Unfortunately, I am an idiot and left a...

2003 Prius with P3191

Seat belt codes

invalid@example.com (ronlewis) — Sat, 04 Apr 2026 13:48:40 +0000

Anyone know if there's a pin to jump in the OBDII connector that will make lights flash on the dash to reveal seat belt codes? The airbag light is on, but I'm not getting anything with TorquePro. This is the car with the driver's seat belt that doesn't retract. This car also was in a front end collision that required a lots of parts to be replaced and left the airbag light on. IIRC, the seat belt was working after I repaired all the body wreck. It quit when I disconnected it to remove...

Seat belt codes

Inverter coolant pump: a cautionary tale

invalid@example.com (Trombone) — Fri, 03 Apr 2026 19:47:57 +0000

After two occurrences of DTC 3130 following 50-60-mile trips, I narrowed the problem down to the inverter coolant pump. There was very little, if any discernible turbulence in the coolant reservoir, a tell-tale sign of a problem. I ordered a new pump, G9020-47022 (without bracket, as the original can be re-used), last Tuesday, UPS delivered it on Wednesday, and the dealer service installed it today. (The fast delivery was due to my close proximity to the Parts Geek warehouse in NJ.)

In...

Inverter coolant pump: a cautionary tale

seat belt

invalid@example.com (ronlewis) — Wed, 01 Apr 2026 21:04:36 +0000

I pull all the interior out of these cars when I buy one, clean it down to the metal, and scrub the carpets real good. Cleaned up many Gen1s without a problem, until this one car. When I went to put the interior back together, the driver's front seat belt no longer retracts, so it's real long and laying around the cabin.

What did I do wrong? It worked fine before I took it out. I expect it has something to do with the restraint system. The (IIRC) airbag light is on.

I have another...

seat belt

Li-ion cells from RAV4 to Prius gen1

invalid@example.com (MArcin91t) — Tue, 31 Mar 2026 21:49:00 +0000

I recently owned a 2000 Prius 1st Gen with a damaged HV battery. It turned out that one cell almost exploded (the side of the battery melted). Obviously, corrosion and voltage distortion on the BMS caused the problem. I replaced that cell with one from a 3rd Gen Prius (all cells balanced, of course), and the battery works.

However, I noticed that the other cells weren't very good either, so I started considering an alternative.

I noticed that you can buy a complete Li-ion battery from a...

Li-ion cells from RAV4 to Prius gen1

car pulls to the right

invalid@example.com (ronlewis) — Mon, 30 Mar 2026 19:10:33 +0000

and there's a slight ticking sound when the brakes are applied over the last few mph. No ticking if I just coast to a stop, or if I use the emergency brake only.

I know, I hate problems that don't throw a code. Using the sniff test to diagnose is a red flag. It doesn't help that I'm also hard of hearing, and don't always wear my hearing aids. I recall it sounding worse at times, the ticks louder, but maybe I just had my aids on that day. Now, it's started pulling, so I need to identify...

car pulls to the right

amateur question about front strut install

invalid@example.com (ronlewis) — Wed, 25 Mar 2026 00:10:03 +0000

the stabilizer bar link doesn't line up with the hole on the new strut, a couple of inches apart. How do I lower the link? I bolted the strut in and jacked on the rotor, it didn't want to go any higher. I gotta do the other side as well - did I do something wring when taking the strut off that allowed the stabilizer bar to rotate up so far?

Cold start : cuts out after ~7 seconds. Did this once every few months, but now totally dead.

invalid@example.com (landspeed) — Sat, 21 Mar 2026 19:42:42 +0000

I posted a thread about an issue I had with my car recently. Got mini VCI today, also realised something important. The problem is quite different from what I thought, hence : I need to make this thread

Background : I bought this car (2003 Prius NWH11) 2019, with a battery fault. I built a battery with NWH20 modules (I had two spare NWH20 batteries, one of which was a bit dubious). The battery worked fine. I lost my Windows install with TechStream, and my OBD2 scanner worked with all cars...

Cold start : cuts out after ~7 seconds. Did this once every few months, but now totally dead.

AC compressor locked up

invalid@example.com (ronlewis) — Sat, 21 Mar 2026 01:21:38 +0000

A buddy's Gen1 had the AC compressor lock up. What parts should be replaced? I know it needs a compressor. Probably the desiccant bag? Should I be worried about the condenser or evaporator core? Do these have an orifice tube, accumulator, etc? The evaporator looks like a PITA to replace.

engine can not start Prius Gen1 2003

invalid@example.com (joegr) — Wed, 18 Mar 2026 18:25:59 +0000

HV battery has been reconditioned, fuel pump checked for corect pressure, fuel injectors cleaned but still not start. Now checking oxygen sensors and see. Any suggestions? 212k km