RIPTEC

I just went to Auto Zone and ran diagnostics. It pulled 2 codes... P0420 & P1259.

P0420 definition - Catalyst system efficiency below threshold bank 1

P1259 definition - VTEC system malfunction

Has anyone ran into these codes before, and what did you do to fix them?

jdowen2

Change your O2 sensors and check your oil level.

RIPTEC

I changed the front O2 sensor about a year ago, do you think it is still good? I've never changed the one by the cat. I just checked the oil the other day and the level was fine, but I do need an oil change bad that's for sure.

RIPTEC

So, I'm still trying to figure out this p1259 vtec malfunction! I had the oil changed and it is fine. Based on my research, I've found that it could either be bad vtec solenoid, bad vtec pressure switch, or bad oil pressure switch. My question is... I'm not throwing an oil light on the dash at all, so can I eliminate the oil pressure switch completely?

SpokaneSpeed

P0420 usually comes up for a bad/clogged cat, or a bad REAR o2 sensor. The rear o2 sensor compares its readings to the front o2 sensor to monitor catalyst efficiency. Unfortunately if the rear o2 sensor readings are bad/off, the ECU will believe that the catalyst is not functioning properly.

Diagnose the P1259 issue before bypassing oil pressure switch. If you determine that is it as bad pressure switch, you can easily replace it, OR if you really want you can bypass it. Don't start trying random things unless you have a definitive diagnosis (RULE NUMBER 1).

Shmallow

the P0420 indicates a "worn" out cat, not necessarily a bad sensor.

clear the code and drive around until it warms up. use VTEC. if the code isn't back there could just be a loose wire or intermittent failure. check all of the wires to be sure. if it does come back on, then like you found in your research it's either the VTEC switch or the solenoid.

GhostAccord

9 times out of 10 it has been my experience that the sensor goes bad long before a catalyst wears out... Just saying! Unless your car has been burning oil and/or coolant for an extended amount of KM/Miles. Then that would cause the catalyst to wear out quicker.

Change your oil.... clear the codes and see what happens. If the code comes back check your connectors and test the sensors and wires. Don't just replace sensors because you think they are to blame. Takes all of 5-10 minutes to test the sensor and could save you in the long run.

SpokaneSpeed

Agreed.

RIPTEC

I just noticed that the top of the v-tec solenoid seems to be leaking some oil. Could this be throwing my p1259 code? Now I'm starting to wonder if the screen is clogged or the seals are bad... and simply replacing the seals would fix that code and fix the bogging down of my engine after running it for a little while.

GhostAccord

The P1259 is an electrical issue, a short or open with the solenoid or pressure switch, if so equipped.

Leaking oil might cause a lower pressure issue but not usually an electrical issue. That being said you should probably replace the upper gasket on the solenoid and the gasket filter for the assembly.

Have you tested the switch and solenoid for continuity? Could be a loose wire or it could be a faulty component. Switch, solenoid wires or ECU. Cheapest to actually trouble shoot these parts than to guess at what could be wrong and aimlessly throw parts at the issue.

bairdandrew77

Go outside and make sure the vtec solenoid connector is plugged in. vtec stopped working one day in my car and it turns out I just didn't plug it in all the way