Error codes confuse me

[crespoh69]

Hello guys, new to the forum and need help diagnosing a problem our 4Runner is having. Using an android phone app called Torque I keep getting error codes P0505 and P0420, from the description on DTC I get the following codes:

Generic
Number P0420
Type Powertrain - Auxiliary Emission Controls - ISO/SAE Controlled
Description
Catalyst System Efficiency Below Threshold
Location Bank 1
Link

and

Generic
Number P0505
Type Powertrain - Vehicle Speed, Idle Control, and Auxiliary Inputs - ISO/SAE Controlled
Description
Idle Air Control System
Link


Having changed out the IACV recently on my miata the 2nd code seems to be a simple enough fix if cleaning doesn't fix it but what about the 420 code? Is that the O2 sensor or is that the CAT? I know my dad recently changed out an O2 sensor last year.

 

[TheDurk]

P0420 is usually one of three things: exhaust leak before the second sensor, bad rear O₂ sensor, bad/damaged cat. So first check for exhaust leaks and eyeball and thump the cat to check for a loose honeycomb or other signs of death. If all looks okay and no leaks, if your rear O₂ is beyond 70K I would just change it. If the sensor is relatively new, find someone who can do a live scan of the sensor output to better diagnose between cat and sensor. Or just gamble and change it. ONLY use Denso replacements.

If you have to change the cat or cats, prepare for $$.

If your dad just changed a sensor, it may well have been the front one. In which case, it is normal for the rear to die shortly afterwards. The front dies first because the gases are hotter up there.

Welcome to the forum! You'll get better help if you put vehicle info in your sig, it saves us having to ask.

 

[techno]

The most common cause of the P0420 code is the A/F sensor (bank 1 sensor 1). This is sensor is slightly different to the o2 sensor and it is the 1st sensor in the exhaust system on cali spec vehicles. It's the one before the cats.
The o2 sensor is the one after the cats (bank 1 sensor 2) and is also a common cause for this error code.
It's very easy to test if you have a multimeter. I highly recommend testing them so you buy the correct replacement first time around as the a/f sensor is almost double the price of the o2.

 

[Limited2K]

P0420 is usually one of three things: exhaust leak before the second sensor, bad rear O₂ sensor, bad/damaged cat. So first check for exhaust leaks and eyeball and thump the cat to check for a loose honeycomb or other signs of death. If all looks okay and no leaks, if your rear O₂ is beyond 70K I would just change it. If the sensor is relatively new, find someone who can do a live scan of the sensor output to better diagnose between cat and sensor. Or just gamble and change it. ONLY use Denso replacements.

If you have to change the cat or cats, prepare for $$.

If your dad just changed a sensor, it may well have been the front one. In which case, it is normal for the rear to die shortly afterwards. The front dies first because the gases are hotter up there.

Welcome to the forum! You'll get better help if you put vehicle info in your sig, it saves us having to ask.

Not to thread jack, but I'm having the same issue with a P0420, I have a new cat (stock was stolen) with less than 15,000 miles on it, and I just replaced the rear sensor to try and fix the code. Does this mean the only other option is an exhaust leak?

 

[TheDurk]

Not to thread jack, but I'm having the same issue with a P0420, I have a new cat (stock was stolen) with less than 15,000 miles on it, and I just replaced the rear sensor to try and fix the code. Does this mean the only other option is an exhaust leak?

Was your replacement cat a Toyota part? Some aftermarket cats can't keep the ECU's happy. Was the new sensor a Denso? Other makes can cause problems. Sometimes the front sensor is the culprit. Other than that, and absent any other codes, the only alternative is the URD simulator to fool the ECU into not throwing the code.

...as far as I know, anyway...

 

[crespoh69]

P0420 is usually one of three things: exhaust leak before the second sensor, bad rear O₂ sensor, bad/damaged cat. So first check for exhaust leaks and eyeball and thump the cat to check for a loose honeycomb or other signs of death. If all looks okay and no leaks, if your rear O₂ is beyond 70K I would just change it. If the sensor is relatively new, find someone who can do a live scan of the sensor output to better diagnose between cat and sensor. Or just gamble and change it. ONLY use Denso replacements.

If you have to change the cat or cats, prepare for $$.

If your dad just changed a sensor, it may well have been the front one. In which case, it is normal for the rear to die shortly afterwards. The front dies first because the gases are hotter up there.

Welcome to the forum! You'll get better help if you put vehicle info in your sig, it saves us having to ask.

Thanks for the VERY detailed reply, as for CAT being a pain on the wallet yeah I know lol my dad's CAT was stolen on his T100 last year and not only did we have to worry about the drive to a shop in a heavily crowded cop area we had to put down money on a brand new CAT too

 

[crespoh69]

OK, I was actually able to force the car to at least start the issue. When doing a left uturn the car will begin to want to turn off again which leads me to believe that the valve is to blame. My parents and sister have all encountered the problem when sitting at a light but I was able to get the car to start to turn off while turning...does this seem like the valve to anyone else?

 

[techno]

For the P0505 code, read through this FSM data. It will help you troubleshoot the problem.
http://www.ncttora.com/fsm/1996/SIL...02rmsour/2002/024runne/di/eg5vzfe/cip0505.pdf

 

[Limited2K]

Was your replacement cat a Toyota part? Some aftermarket cats can't keep the ECU's happy. Was the new sensor a Denso? Other makes can cause problems. Sometimes the front sensor is the culprit. Other than that, and absent any other codes, the only alternative is the URD simulator to fool the ECU into not throwing the code.

...as far as I know, anyway...

Sorry, should have specified. The sensor was a Denso replacement, and the cat was an aftermarket magnaflow, which seems to be the culprit. What's interesting is the CEL went off for about 50 miles the other day (after sensor replacement, code reset, then CEL came back on) then returned. If the front sensor was a contributing factor, wouldn't my mpg be affected? I'm consistently over 20 mpg. Or can it be failing to bring on a CEL, but not affect mileage?

EDIT: Also it is a solo P0420 code.

 

[fastolds]

It was my experience that a p0420 means the cat is below specs. My 98 has cali emissions and my only viable option at the time was to get a OEM part. Apparently there is a big difference between cali and fed emissions.

Adam

 

[TheDurk]

It was my experience that a p0420 means the cat is below specs. My 98 has cali emissions and my only viable option at the time was to get a OEM part. Apparently there is a big difference between cali and fed emissions.

Adam

As far as I know, the stricter Cali. spec only started in '99. Do you have one or two cats? And the rear sensor can definitely cause the p0420--probably happens more often than the cats. It certainly happened on my '99 Cali.

 

[TheDurk]

Sorry, should have specified. The sensor was a Denso replacement, and the cat was an aftermarket magnaflow, which seems to be the culprit. What's interesting is the CEL went off for about 50 miles the other day (after sensor replacement, code reset, then CEL came back on) then returned. If the front sensor was a contributing factor, wouldn't my mpg be affected? I'm consistently over 20 mpg. Or can it be failing to bring on a CEL, but not affect mileage?

EDIT: Also it is a solo P0420 code.

I didn't say it was likely in your case, but it is a possibility listed in the FSM. In your case, I would certainly suspect the Magnaflow.

 

[fastolds]

Yeah mine is definitely a cali truck. But it is also a 4 cylinder. I have 1 big, expensive cat. Mine was replaced almost 2 years ago. Still running the OEM rear sensor.

With error codes, it could be anything listed- the code just points you in the right direction.

thanks
adam

 

[TheDurk]

Yeah mine is definitely a cali truck. But it is also a 4 cylinder. I have 1 big, expensive cat. Mine was replaced almost 2 years ago. Still running the OEM rear sensor.

With error codes, it could be anything listed- the code just points you in the right direction.

thanks
adam

You have a 50-state truck. Thanks for the tip about codes; it will make my next 11 years of working on 4Runners easier.

 

[crespoh69]

Would either code though be the cause for the engine just turning off on me? If it were the fuel pump, would there be an error code too?

 

[TheDurk]

Would either code though be the cause for the engine just turning off on me? If it were the fuel pump, would there be an error code too?

Well, you obviously have the '01-'02 throttle-by-wire system. The P0505 means something is wrong in that subsystem. I have never worked on one, but I suspect more may be going on than just the IAC valve. In any case, Techno pointed you to the right place for troubleshooting that code. I'd cure that first, before I looked elsewhere. That almost certainly will resolve your problem. P0420 would not cause that unless your cat was completely plugged--unlikely, and it would not be intermittent--it just would die and stay dead.

Fuel starvation would usually throw p030X (misfire) codes or p0171 (System Too Lean). That said, counting on codes NOT thrown can be risky. The diagnostic system is far from perfect. But definitely go after the P0505 and then see how it goes.