Toyota Repair Problems? Ask a Mechanic for Answers ASAP
Those codes indicate two different areas of concern;
P0420 sets when the onboard computer detects catalytic efficiency to be below the expected threshold. Causes can be...
Exhaust system leak. Defective A/F sensor. Defective heated oxygen sensor No. 2. Defective catalytic converter.
P0440 and P0442 set when the onboard computer detects a leak in the Evaporative Emission System. Causes can be...
Damaged, disconnected or blocked vacuum hose(s). Fuel tank cap is installed incorrectly. Defective fuel tank cap. Damaged fuel tank. Defective charcoal canister. Vapor pressure sensor circuit is open or shorted. Defective vapor pressure sensor. Defective fuel tank overfill valve. Defective ECM.
I can help you take care of this issue in one of two different ways: One is to replace system parts one by one until one of those parts fixes the problem; the other involves you having access to tools that you must use under my guidance to perform a comprehensive diagnosis that will surely reveal the root cause. Please let me know which way you choose so we can start.
What kind of tool do I need?
For the P0420, you'll need a fast digital voltmeter (click here for example from Walmart) to test the downstream Oxygen sensor.
For the P0440 and P0442, you'll need the same type of voltmeter to test the solenoid valves and a manual vacuum pump/gauge (click here for example from Harbor freight) to test for leaks.
Since time for us is of the essence, please familiarize yourself with the use of both tools before the start of the diagnosis.
Ok, I'm ready, please give me instructions.
Ok. Starting with P0420, get the engine up to normal operating temperature, turn all accessories off and measure voltage at the Black wire going to the sensor connector. Voltage should normally stay at an almost fixed voltage under 1.0 volts. In this case, the onboard computer has detected voltages switching rapidly up and down within the 1 volt range. If your checks reveal the latter is true, then the catalytic converter is bad and needs to be replaced.
The other two codes will take much longer to diagnose and I'm way past my usual log-off time of 8 PM Atlantic Standard Time. I'll be back tomorrow after 2 PM AST to continue our diagnosis.
Wouldn't be easier and faster with an scanner?
A scan tool can only display whatever data the onboard computer is transmitting through the data link connector, it can't measure the actual circuit voltage like a voltmeter can. The best way to find out if the onboard computer is either getting or generating a bad signal is by comparing the PID on the scan tool to the actual circuit signal as read with a voltmeter or better yet a scope.
Hey, I just noticed your excellent history with our site, and based on that history I'm going to guess you're probably a fellow mechanic working hard to make a living out there. So, I can share with you the fact that 99.99% of the times codes P0440 and P0442 come up on a Toyota it ends up being one of the vacuum switching valves that are part of and sold with the charcoal canister assembly (about $350 last time I checked). If you look at it closely, you'll see there is a way to take the old one out and sneak the new in by just dropping one corner of the tank.
Let me know if there's anything else I can do to help.
Thank you.. are you talking about the overfill check valve?
No, usually the ORVR will set code P0446. I'm talking about the vacuum switching valve for the pressure switching valve as being the one causing P0440 and P0442 most of the times.
Toyota has had different EVAP systems, all with different issues. If you want to learn more about this topic, there are a couple of TSBs out there that try to explain the whole thing (notice I say "try to explain" - they don't do a good job of it in my opinion) - TSBs are EG005-01 and EG013R-03.
Ok let me check it out
Cool. I'm going to be off-line until tomorrow. I'll check on you then.