Holy Codes!

[Capocaccia]

I recently replaced all the lights in my dash cluster and my check engine light was on so I went to get it checked an heres what shows up. Please elaborate on these if you can. (you know, put them in retard terms) Also, please let me know how much of this I can fix myself to save some cash.

P0171
The PCM has determined that during testing the fuel system for bank 1 was too lean.

P0125
The PCM has determined that the amount of time it took for hte coolant temperature sensor to reach an input value consistent with the closed loop operation was too excessive.

P0133
The PCM has determined that the response time for oxygen sensor 1 in bank 1 was too slow during testing.

P0401
The PCM has determined that there is insufficent flow in the exhaust gas recirculation system.

P0420
The PCM has determined that the catalyst system for bank 1 is below threshold for the current engine operating conditions.

P0753
The PCM has deterrminted that a short to ground, a short to battery, or an open circuit condition in the electrical circuit for shift solenoid "A".

 

[Whipp]

P0420 and P0133: The 1995+ 80 series has two oxygen sensors. The first one is primarily used to ensure that the correct air/fuel ratio is being maintained. The second one is used to ensure that the catalytic converts are working properly. P0420 indicates that the catalytic converter isn't doing its job anymore, but is usually caused by the O2 sensors failing, and not the catalytic converter. P0133 shows that you have a slow oxygen sensor (I think the post cat converter sensor, but am not quite sure). I had both error codes and replacing both of the oxygen sensors fixed them. This job is pretty easy, two nuts per sensor and then you unplug the wiring harnesses. The nuts that hold on the O2 sensors are usually heavily corroded (read - totally rounded off) and need to be replaced. Applying penetrating fluid for a few days to a week before doing the job makes it easier. This comes up a lot on the board and is well documented.

P0171: The pre-cat oxygen sensor is reading that the exhaust gas has too much oxygen. The ECU has probably reached the limites of the corrections that it can make, or has passed a certain threshold level of corrections. With the other oxygen sensor error, I'd guess that this error may be related to the bad oxygen sensor. Another likely candidate would be the MAF sensor, which measures the amount of air going into the engine. It's easy to replace too, but may be expensive. I'd replace the O2 sensors, clear the codes, then see if it comes back. Does your engine ping any or run hot?

P0401: For emissions purposes, some exhaust gas is recirculated (EGR = Exhaust Gas Recirculation) into the intake manifold. This is primarily done to reduce oxides of nitrogen (NOx) emissions by reducing the combustion temperature. This error is pretty common (I had this one too) and there are many threads on the board about it. The most likely components to fail and cause this error are the vacuum switching valve for EGR, the EGR modulator, and plugged vacuum lines in the EGR system. All of these components are replaceable without too much difficulty, though the VSV can be a pain to get to as it is underneath the intake plenum.

P0125: The ECU thinks that your engine is warming up too slowly. I have no experience with this, but first I'd check the coolant temperature sensor and make sure that it's plugged securely into the wiring harness. The 80 series temperature gauge (on the instrument cluster) is pretty lame (a huge center "dead" zone), so it probably won't help you much. Off hand, it may be possible that because of your oxygen sensor issues, your engine is running very rich (how's your gas mileage?) and just warming up slowly, in which case replacing the oxygen sensors may fix this, but that's pure speculation on my part.

P0753: I have no idea. How well does your LX shift?

How many miles are on your truck? Any idea if your oxygen sensors have been changed yet? (I'm guessing 150K or greater and still the original sensors.)

 

[Capocaccia]

130k miles. Original oxygen sensors. And as for the gas mileage, well, lets just say its horrible. Im talking tops 11 to the gallon. I did the whole reset the trip meter thing and then I was getting 11.6. So pretty much waht Im hearing is replace the oxygen sensors and It might correct all the exhaust problems? Also, No, my engine does not ping or run hot. And my LX shifts fine right now. It has a hard time when in cruise control sometimes but its rarely in it anyways.

 

[Whipp]

Replacing the O2 sensors would be my first step. I'd guess that it would take care of P0420 and P0133, and maybe P0125 and P0171.

There are a lot of threads that cover this, I'll link to a post I wrote up shortly after fixing my issues:
https://forum.ih8mud.com/showpost.php?p=754586&postcount=10

 

[KingOfFools]

P0171: The pre-cat oxygen sensor is reading that the exhaust gas has too much oxygen. The ECU has probably reached the limites of the corrections that it can make, or has passed a certain threshold level of corrections. With the other oxygen sensor error, I'd guess that this error may be related to the bad oxygen sensor. Another likely candidate would be the MAF sensor, which measures the amount of air going into the engine. It's easy to replace too, but may be expensive. I'd replace the O2 sensors, clear the codes, then see if it comes back. Does your engine ping any or run hot?

The p0171 on Toyotas can be a couple of different things, the most common of which is a vacuum leak. Other possibilities are a bad mass air flow meter, ( not very common and big $$$), or an exhaust leak upstream from the #1 o2 sensor. I had a 95 in the shop last week with the upstream o2 sensor blown out of it, and the only code I got out of it was the p0125, so a bad sensor could have caused both of those. If you have never put o2 sensors in it, I would do that first, and check carefully for vacuum leaks.

 

[okefenokeefzj80]

I would start by unscrewing my gas cap and then screwing it back on and make sure it clicks 5 or 6 times. I've had a vacuum seal leak before and that was the culprit. It will take about 30 full shifts to make it come off.