OBD code P0203/0303 - Toyota Nation Forum : Toyota Car and Truck Forums
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post #1 of 10 Old 03-12-2018, 09:02 AM Thread Starter
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OBD code P0203/0303

I have a 2005 4Runner w/ 4.7 V8 w/ 84k original miles. A fewweeks ago the check engine light came on and the fault code came back as 0203or 0303; I don't recall exactly but it was a "misfire on cylinder 3".In the past, when this has occurred on other vehicles, I have replaced the coilpack and the code clears. So, I replaced the coil pack and cleared the code;everything was fine but it came back again a couple days later. I should haverealized that the truck still had the original plugs, and they were longoverdue to be changed according to the maint schedule. So, I replaced them andcleared the code. The truck, again, was fine for a couple days but has now comeback on again and I'm perplexed as to what it could be.

If it is fuel injector related, is there any way to check orclean an injector? Can I try running FI cleaner thru it? Any other ideas?

The day when it first happened, I noticed that when Istarted the truck, the battery/starter gave a momentary hesitation as it wasbeing started. I thought it was odd and the code came up shortly thereafter.The battery was also original, so I figured I might as well replace it, too,b/c I noticed it getting weaker thru the winter months. But, I wondered ifthere could have been a momentary pulse or hesitation that could have screwedw/ the ECM that caused a false code....just fishing at this point.

Also, what is the best way to clear the code? I justdisconnect the battery for a few seconds to reboot the system; it erases thetrip meter, fuel mileage settings, and clock, but the radio stations areretained. Is there something else I should do to clear it? Again, justfishing.
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post #2 of 10 Old 03-12-2018, 10:28 AM
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P0203 likely electrical injector/circuit problem.
Test for proper voltage/resistance to determine problem or swap injector to see if error code follows.
Of course try fuel cleaner if nothing else, can't hurt.

Regarding suspect battery, if cranking voltage drops below 9v, time for new battery.
Best way to clear codes is to first read error code/freeze frame data with scan tool, then clear codes.
If no scan tool then disconnecting battery for a minute or so should do it.
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post #3 of 10 Old 03-27-2018, 12:50 PM Thread Starter
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I have not tried switching injectors to see of the P0303 code follows the injector or stays with the cylinder; but, I did put an OBD2 scanner on it and watched live and freeze frame data. It seems like there may be an issue (?) with one or more of the fuel bank sensors, but I am not sure how to interpret the data and I'm not 100% sure where those sensor are located (I can't find it in the manual). Here is what I am seeing:
* After clearing the code, it usually takes 2 days to come back. The code always appears at low speed or idle.
* SHRTF1 (Short Term Fuel Trim Bank 1) always shows -3.9% to 3.1%
* SHRTF2 (Short Term Fuel Trim Bank 2) always shows -3.1% to 2.1%
* SHRTF3 (Short Term Fuel Trim Bank 3) always shows -98.4%
* SHRTF4 (Short Term Fuel Trim Bank 4) always shows -98.4%
* LONGFT1 (Long Term Fuel Trim Bank 1) always shows -7.0% to -3.1%
* LONGFT2 (Long Term Fuel Trim Bank 2) always shows -0.8% to -0.08%
* LONGFT3 (Long Term Fuel Trim Bank 3) always shows -98.4%
* LONGFT4 (Long Term Fuel Trim Bank 4) always shows -98.4%
* SHRTFTB2S2 (Short Term Fuel Trim Bank O2 Sensor Bank 2 Sensor 2??) always shows 99.2%


Obviously, there appears to be something going on with fuel bank 3 and 4, but I'm not sure what the next step should be. Anyone have any thoughts?
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post #4 of 10 Old 03-27-2018, 02:11 PM
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Can you post the freeze frame data?
The fuel trims are normal enough if they stay within plus/minus 10 at all engine loads.
Ignore info for banks 3/4.
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post #5 of 10 Old 03-27-2018, 02:43 PM Thread Starter
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I was keeping a spreadsheet of the data to compare when it happened. Attached is a pdf. Can you open it? If not, I will have to do screen shot and convert to a jpg. Thanks.
Attached Files
File Type: pdf OBDII Data.pdf (94.0 KB, 17 views)
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post #6 of 10 Old 03-27-2018, 03:38 PM
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Looking thru the data, see P0303 at low engine load.
Since you have changed coil/plugs next would be fuel injector.
Have you tried adding injector cleaning yet?
May be worth to have a shop do a concentrated cleaning.

Have no experience with the V8 layout so don't whats involved swapping injector.

Does the P0303 cause the check engine light to flash for a while or just turn on?
P0203 also sets?
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post #7 of 10 Old 03-28-2018, 08:25 AM Thread Starter
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Thanks for the feedback. Yes, my next thought was to swap inj 3 and 1 and see if the code follows the inj or the cylinder. I haven't tested the inj resistance, either, which I should be able to do w/o removing it, but that just indicates that the solenoid is potentially OK. I just ran some FI cleaner with the last fuel up and it didn't change anything; which I was not expecting it to do so, so I thought about the concentrated cleaner route IF it really is isolated to the injector.


I was looking at the live data this morning and noticed that there is nothing associated w/ short/long term trims for banks 3/4. So, I guess I am to assume that there are only the 2 banks and the freeze frame data for 3/4 are only placeholders? That now makes sense. However, the live data still shows SHRTFTB2S2 at ~99%. I know enough about the OBD2 system to be dangerous, but I believe this data point is associated w/ O2 sensor #2?


Also, I noticed something really odd over the weekend. I live in central PA; the weather was decent over the weekend, so I washed the truck to get the road salt off of it. It had been awhile since I last washed it, so I sprayed up underneath the wheel wells and along the frame to try to get as much of the crap off of it. I also opened the hood and rinsed the engine compartment down (which I have done on occasion since I've owned the truck). The handheld scanner I have has green, yellow, and red LEDs on it that indicates the overall system function/status. Since I started to monitor this gremlin, the yellow LED has always lit; indicating that there is a problem w/ the system but not enough to cause a code/fault and switch the red LED on. However, when I connected the scanner and drove to work the next day after washing it, the green LED was on. After work, when I started the vehicle, the yellow LED was back. The yellow LED stayed lit while I drove to work the next day but it had started to rain. It was still raining when I left work, but the LED was now green. The next day, the roads were dry and the LED was back to yellow.


So, now I'm wondering, did the humid, moist air affect the trim sensor, or do I have an incomplete connection someplace and the water/moisture helps to maintain contact until it dries out? This is really maddening. Any idea where those trim sensors are located?


BTW, the check engine MIL does not flash and the code has always been P0303....I initially thought it was 0203 but that was wrong.
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post #8 of 10 Old 03-28-2018, 10:14 AM
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"However, the live data still shows SHRTFTB2S2 at ~99%. I know enough about the OBD2 system to be dangerous, but I believe this data point is associated w/ O2 sensor #2?"
Ignore the SHRTFTB2S2 at ~99%.

Regarding the colored lights on your scanner, can you relate them to your check engine light/P0302?

"So, now I'm wondering, did the humid, moist air affect the trim sensor, or do I have an incomplete connection someplace and the water/moisture helps to maintain contact until it dries out?"
Possible on both accounts.

The A/F sensors are before the cat converters and the O2 sensors after the converters.
According to the data they are operating normally.

May be time to measure/swap injectors.
Auto diagnostic shop could make short work of the injector question by monitoring the injector current during a misfire.
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post #9 of 10 Old 03-28-2018, 11:37 AM Thread Starter
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According to the manual for the scanner:

Green LED Display - indicates the engine system is working normally (all monitors on the
testing), and no DTCs are found.
Yellow LED Display - shows the tool finds a possible problem. Pending DTCs exist or/and some of
the vehicle’s emission monitors have not run their diagnostic testing.
Red LED Display - indicates there are some problems in one or more of the vehicle’s systems. In
his case, the MIL lamp on the instrument panel is on.


I had been consistently seeing a yellow light until the MIL can on, then it would switch to red indicating a fault. But, as I said, it has shown green now when higher humidity is present or something has gotten wet.


It's been tough to tell if the misfire is intermittent or continuous. I'm not noticing any major difference in performance or gas mileage so it makes me think it is an intermittent problem at low load/speed. I would think if it is a fouled injector it might be more noticeable. Like I said before, I am going to check the resistance on the injector to see if it is within spec and how it compares w/ others, but I think if it is out of spec, that is only going to tell me that I in fact have a bad solenoid on the injector. If it is in spec, that isn't going to tell me with certainty that the injector is "good." Thanks again for the feedback!
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post #10 of 10 Old 03-28-2018, 01:32 PM
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Since you don't notice much difference in performance/mileage/check engine light doesn't flash and fuel trims close normal, not doing any engine or converter cat damage.

Let us know the outcome.
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