P0420 Diag

[contrail_25]

Cardoc: thanks for the explanation and vid. Wish I had a mechanic like you in my area. I had the P0420 come on again, 2 miles after filling with a different brand of gas while on a road trip this weekend. So far only the gas sold on base hasn't caused the code to come on. Maybe that's the key, not sure. Kinda scratching my head.

Anyways, I had my scanner and got the following off of it:

Codes(2):

P0420 Cnf ModE1
Catalytic System Efficiency Below Threshold Bank1

P0420 Pnd ModE1
Catalytic System Efficiency Below Threshold Bank1

Snapshot data (in its entirety):

ENG SPEED: 2300rpm
CALC LOAD: 18.8%
MAP: 59.0("HG)
COOLANT: 83(F)
ST FTRM 1: 7.8%
LT FTRM 1: 0.0%
VEH SPEED: 94 (I was going 65 when it came on, so not sure why this is so far off)
FUEL SYS 1: CLOSED
FUEL SYS 2: N/A

[cardoc]

That's a snapshot of the freeze frame at the time the problem was first "seen" by the computer. Depending on how long the engine was running when this occurred, I see the temp is low. Within 8 minutes the engine temperature should be up to operating temp.

The ECM turned the light on after repeated occurrence of the fault. The MAP pressure is high, so I can assume its not a turbo running high boost, you may want to look in to that.

So if your scanner shows live data you need to run the car from dead cold and look at the temperature, MAP, front AF and rear O2 sensor output. The temperature needs to get up to 190-200 and average in that range. Your car runs AF sensors in the front, so you will be looking for the same values as I have in the VDC scan video and midrange to low O2 values. If your engine temp is remaining low, change the thermostat, then while you are verifying proper function and engine temp, watch the sensor readings for a change.

You have the advantage in owning a scan tool. The freeze frame is good. It's better if it reads and outputs data.

Also, the short term trim is high, but with the temp and speed of the car, that would be normal. If your temp was up, it wouldn't be that high.

[cardoc]

I've had my second cup of coffee and looked at the frame again. 2300 rpm, 94 mph and the MAP readings seem to be an issue either with the car or your scanner. If the values are correct and your scanner isn't screwing the numbers, check your battery, grounds and alternator output. Still verify proper engine temperature and look at the values of the sensors.

[contrail_25]

2300 rpm - correct.
94 mph - bad...I was going 60-65. However, 94kph is about 61mph. Maybe there is a scanner conspiracy? j/k
59 inHG - yeah not a turbo.
83F - car was running about 5-10 minutes and it's cold here.

My scanner doesn't do live data, I'm going see if the shop on my base has one I can use. Or I can try to get an adapter and use that FreeSSM program to watch live readings.

[plain OM]

I can try to get an adapter and use that FreeSSM program to watch live readings.

FreeSSM displays data in a simple format but doesn't have more visible displays or graphing, and doesn't record the data for subsequent analysis. For that, perhaps look into Romraider Logger. (It has these more useful data display/captures, but I'm not sure if the list of definitions includes the 2001 2.5.)

[cardoc]

Originally Posted by plain OM

Both the




FreeSSM displays data in a simple format but doesn't have more visible displays or graphing, and doesn't record the data for subsequent analysis. For that, perhaps look into Romraider Logger. (It has these more useful data display/captures, but I'm not sure if the list of definitions includes the 2001 2.5.)

Yes it does. Use the 2002 Impreza USDM definitions.

[plain OM]

That's good. So there's a few low-cost options for examining what's happening.

Thanks cardoc.

Hope contrail_25 follows up on this. Going to be another interesting P0420 analysis.

[cardoc]

Originally Posted by plain OM

That's good. So there's a few low-cost options for examining what's happening.

Thanks cardoc.

Hope contrail_25 follows up on this. Going to be another interesting P0420 analysis.

If that MAP sensor is actually sending 59 inHg to the PCM, that's where the problem lies. The ECM is trying to match the fuel to the air, then the AF is sending different values so it finds the middle. Running rich and low engine temperature will lead to a failed CAT if it persist.

Gotta see the data with an accurate scanner.

[plain OM]

As contrail_25 noted,

94 mph - bad...I was going 60-65. However, 94kph is about 61mph.

and I wonder if in addition to the speed conversion, both the coolant temperature and MAP might be consistent with different units.

For example, the "83" for coolant temperature could be Celsius, which would be about 180 F, and the 59.0 for the MAP could be kPa, which would equate to 8.5 psi.

Would these be more in line with what would be expected? I looked back at a Romraider log I have for my engine, running at approx 100 kph or 63 mph with outside temp around 9 C or 48 F. (This was a "steady state" situation -- we had been driving for some time when the log was made.) The coolant temp was at 87 C, or 189 F, and the MAP was around 8 psi or 55 kPa. Rather similar to what contrail_25 reported.

[contrail_25]

cardoc: the MAP/IAT sensor had thrown a code (P0113) with the first instance of my P0420 experience.

plain om: interesting thought with the conversions. 59 inHG is about 29 Psi, which is kinda high. So maybe it's not inHG (as my reader shows) and actually kPa like you suggested? Could be on to something here.

It might be into next week before I can really work on this. Busy learning a new aircraft these days.