2000 Corolla P0420 - Toyota Corolla, Chevy Prizm (1998-2008)

Group

I have a 2000 Toyota Corolla and installed a 2004 Corolla engine two weeks back. About 5 minutes after driving the car the code P0420 came up. I have had the code reset several times only to have it return after a few miles driving. This code never came up with the old engine, this only started after installing new engine.

Car was warm when testing the O2 sensors

I have checked the upstream O2 sensor, it has a 4 wire connection

Wire readings

1. Black 1 0.368 volts

2. Black 2 0.058 volts

3. White 0.01 volts

4. Blue 0.1 to 0.8 volts

I have also checked the O2 sensor located after the convertor, it has a 4 wire connection

Wire readings

1. Black 1 13.65 volts

2. Black 2 0.417 volts

3. White -0.017 volts (negitive reading)

4. Blue 0.086 to 0.800 volts (range)

Dont know what the readings should be

Any help would be great

Thanks in advance

Hello and welcome to the forums.

Denso O2 sensor wire colors

Black = heater (+12V or ground, no polarity)

Blue = (+) signal

White = (-) signal (referenced to ground)

As far as output goes - the readings your getting sound about right, except for the heater values for the upstream O2 sensor (should be source voltage on one line and ground on the other). But that is a mute point, as the ones we care around - the blue and white signal lines are swinging from 0.1V to 0.8V. That is OK, but we need to know the rate of change. The upstream (pre-cat) can rapidly switch from low to high voltage levels. The downstream sensor can vary the same about - but much more slowly. If they vary at the same rate - this will set a P0420 code. The causes could be either a faulty O2 sensor (generally the down stream one, but could be both), a bad catalytic converter, bad heater circuit (could be, have to double check the upstream one and verify those voltages), or a exhaust leak (most likely, as you have swapped in a new engine). I'd double check that it isn't a simple leaky exhaust or the connector to the O2 sensor (check the wiring) got chewed up or otherwise damaged during the swap. If the old engine was one of those "oil burners" - there is a good chance that the O2 sensors are fouled and the catalytic converter is plugged. May have just needed a little "tap" to push it over the edge.

I re-checked the front O2 sensor and here are the results

upstream O2 sensor

Wire readings

1. Black 1 13volts

2. Black 2 13 volts

3. White 0.01 volts

4. Blue 0.1 to 0.8 volts

Also check the vacuum and found the following related to a bad cat causing back pressure

Reading at idle is 21psi

Rev the engine and initially the vacuum drops to 15psi, but quickly recovers to 21psi holding the higher rpms

What this tells me is there is little to no back pressure being caused by the cat...not clogged I guess

This forum is great

One last thing

Ive checked and No exhaust leaks

Only thing is the engine seems to idle a little higher than the old engine

New engine only has 325 miles default_smile ....its like a heart transplant

Thanks again for all the help

Those new readings show that the upstream one is reading OK - the voltage on the heater circuit still looks odd. Should be source and ground. Also tough to get a decent reading from the O2 sensor signal lines without running it to an o-scope. With a digital multimeter, hard to tell the shape of the waveform, unless it has a bar graph display like some Fluke meters or if you have an older analog meter laying around.

Cat also seems to be clear - though it is still possible that the catalytic converter is bad. But in 90% of the P0420 code - it is usually something other than the cat. O2 sensors are high on the list - especially if they were replaced with non-Denso sensors. Common issue I've heard with other replacements, Bosch is a common one, is that their impedance is different than the Denso ones - could cause a shift or bias in the signals that could be interpreted as an error condition.

Since you've already reset the CEL and it almost immediately came back - to me sounds likely that one of the sensors (or both) could be toasted or "lazy". The P0420 CEL is only set if the measured signals between the two O2 sensors are too "similar" in shape, which could mean that the catalytic efficiency is reduced. Of course, the ECM assumes that the O2 sensors are working perfectly - if one is toasted, it will set the conditions for a P0420 CEL.

Curious - what was swapped? Just the short block, the whole engine, ECM and transaxle was also swapped? Trying to get more info on this.

On the swap

The 2004 engine is the same as the 2000 engine, the only things you need to change will be the intake and exhaust manifolds. I also used had to use a few on the sensors from the 2000, but only a few were different. The swap was/should have been easy. Just a note, the engine and trans will come out as a unit. Will explain more after work today

Was there something that you wanted to know?

Sounds like you just replaced the driveline (engine and transaxle). I'm assuming that you swapped the ECM from the 2004 over as well? The 1ZZ-FE are very simimlar between the two generations, but there are small differences in the 9th gen motor and transaxle that might be causing you some headaches.

These include a different camshaft profile (more HP with slightly less mid-range torque), plastic intake runners instead of the long aluminum tubular intake runners, a new 32-bit ECU system, modified exhaust/exhaust manifold changes, new gear ratios and new ATF fluid spec(if automatic), differential gear change and new syncro design (if manual), they combined the clutch and brake master cylinders together, cooling fan is ECU controlled, different starter (smaller), and retuned VVTi system.

O2 sensors-wise, they both use the same family of sensors - only in the 2005 model year, they switched to an AFR type of O2 sensor (more expensive and not backwards compatible) and new protocal for the OBD-II system (CAN protocal instead of ISO).

What I did was the following

I got the 2004 engine and swapped the intake and exhaust manifolds, and about 2 sensors that were different.

The trans I got was from a low miles 2000, but it was the engine that I was after (324 miles)

I hoping that the increased hp is not whats causing my issues. I spoke to a shop that does these corolla engine swaps all the time

They told me the engines (2000 and 2004) were about the same, minus the intake and exhaust manifolds

I did order new o2 sensors from rockauto, got them really cheap for OE brand (130 for both)

Im really hoping that this corrects the issue

The only sensor I have not checked is the engine temp sensor, might check that one this weekend

The enigne swap went really easy, keep the engine and trans together

Center your hoist on the engine, this will cause the unit (eng & trans) to lean towards the trans

This will allow you to clear the battery support platform (stupid design)

Once you get the trans past the battery platform attach the top trans mount

The rest of the mounts will fall into place

Note, its implied that the hood is removed

Good description, thanks. Hopefully the O2 sensors will clear that up for you - let us know if that does the trick. So it sounds like you mated the 8th gen trans to a 9th gen engine? The two are from the same family, so most everything will swap over. Be interesting to see what the fuel economy looks like after the swap. The 8th gen transaxle run taller gears than the 9th gen transaxle - so you will be turning lower RPMs at speed.

The car gets about 30 mpg almost all city, about the same as the old setup. The swap was simple...note to all...when doing a swap put the engine and trans in as a unit. You will hook the trans mount - top left side (as seen from drives seat) and then let the unit down. Makes it really simple

Good luck

friendly_jacek

Interesting thread.

Why did you replace the engine/tranny in the first place?