Mauricio Vasquez Problem whith code p0420 my honda accord 2001 motor 2.3lt V-tec Ulev

Negative 36 Volts ? Negative 36 fuel trim ?

1999 Honda Accord Workshop Repair Service Manual PDF Download

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Here is the explanation from engine-codes.com

P1259 Honda Description
The VTEC system activates the VTEC solenoid valve by command from the powertrain control module (PCM), and it charges/discharges the hydraulic circuit of the VTEC mechanism that is installed in the valve system to switch valve timing between Low and High. The PCM monitors oil pressure conditions in the hydraulic circuit of the VTEC mechanism according to the VTEC oil pressure switch downstream of the VTEC solenoid valve. If there is a disparity between oil pressure condition in the hydraulic circuit that is determined by the PCM command, and the oil pressure condition that is determined by the status of the VTEC oil pressure switch, the system is considered faulty and a DTC is stored.

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Usually does. But I check the O2 sensors first. Ohm check them and the wires. Your cats are expensive, I don't won't to misdiagnose.

I had the same problem on my 1999 Honda Accord 4 cyl. It was the ignition switch. I received a letter from Honda regarding a recall on the ignition switch and had it replaced. 3 years after replacement it would turn off again & this time I purchased part from eBaby & replaced it myself. It hasn’t stalled since.

You need to change the oxygen sensor.

P0401- Bad EGR valve
P0420- Most likely cause is a bad O2 sensor(s) at the catalytic converter

Code P0420 probable cause, 1. Secondary HO2S (Sensor 2) or 2.Three Way Catalytic converter.

I would send the car for a smoke test for the emissions leak...Find out where the leak is comming from..Repair it..Reset the codes, then do a drive cycle and see what happens...

P0420 - Catalyst System Low Efficiency