My experience with codes 0300, 0303, 0306, 0125, and 1135

[Supraformance]

My '99 SR5 started running like total crap recently. I was experiencing this terrible hesitation and shake at 1/4-1/2 throttle and any more gas would stop the car from shaking but gave it absolutely no power at all. I couldn't go above 50mph. The CEL came on when this began to happen so I parked the car and just got around to scanning it today.

Codes were:
0300 - Random miss
0303 - Cyl. 3 miss
0306 - Cyl. 6 miss
0125 - Something about insufficent coolant temp in closed loop fuel?
1135 - A/F sensor malfunction


I basically ignored 0300 and figured it was a general code for the problems I was having with cylinder 3 and 6. I also figured 1135 was related to the misfire I was sustaining on two cylinders.

First thing I did was pull the plug out of cylinder 6 and tried firing the car up again. There was no spark. I traced the wire back to the coil on the left side of the motor and sure enough it was connected to cylinder 3. This gave me the idea that the coil on cylinder 3 was bad and since it "piggybacks" over to cylinder 6 that would explain why I was dead on both of those cylinders.

Sure enough I swapped the coil out with a replacement from PepBoys, left all the same spark plugs in, and it fired right up and idled like it should. After a 30 minute drive with no CEL returning, I'm thinking I might have fixed the issue?

I read a lot about guys having problems with these codes and the fix most of the time was a clogged injector. Hope this helps someone who is researching a fix on their own car.

 

[BrianSD_42]

I swapped the coil out with an OEM replacement from PepBoys

I didn't realize PepBoys sold OEM/Toyota parts but perhaps they do. I would think you mean aftermarket or non-OEM.

Based on your description I would say drive it a while longer and report back.

 

[Supraformance]

I didn't realize PepBoys sold OEM/Toyota parts. I think you mean aftermarket or non-OEM.

Yeah my bad, that's what I meant. I've got a lot of projects going on right now.

 

[TheDurk]

You probably cured the P0303 and P0306 and the rough running, but I doubt you cured the P0125 and P1135. That's a 2-trip detection and it probably means a new A/F sensor in your future that will cure both codes. I would expect that P1135 to come back, with or without the P0125. It could also be a bad connection in A/F heater wiring, in which case it could come and go. If it is the heater, it will not heal itself and I don't see how the misfire could trigger it.

If you do need an A/F sensor, don't get it at Pep Boys. Get an OEM Denso off of Amazon.

 

[Supraformance]

Yeah the 0125 and 1135 have come back but the car is still running like a champ. I was thinking maybe the misfire was causing the A/F sensor to freak out and would eventually get over it once I cured the misfire but it looks like I'll have to replace the A/F sensor too.

The 0125 though... I almost want to just ignore it and continue driving with the CEL.

 

[TheDurk]

Yeah the 0125 and 1135 have come back but the car is still running like a champ. I was thinking maybe the misfire was causing the A/F sensor to freak out and would eventually get over it once I cured the misfire but it looks like I'll have to replace the A/F sensor too.

The 0125 though... I almost want to just ignore it and continue driving with the CEL.

The P0125 will disappear when you change the sensor, trust me. It means nothing. The risk is, without a functioning front sensor, you may be sending excess unburned fuel through your cats driving down fuel efficiency and potentially ruining your cats. Without a working front sensor, the ECM has no way to accurately guess the correct fuel/air mixture. Also, it might run well at one temperature, but not at another.

 

[Supraformance]

Thanks Durk, I will report back in a couple days once the sensor comes in. I ordered the OEM Denso sensor from Toyota. Might explain the poor gas mileage I've been experiencing for a while.