Freeze frame data interpretation

What does this freeze frame data below indicate? (I understand the PO 420 error code which has happened twice a month apart. All the readiness codes read fine.)

11/23 PO 420 catalyst system efficiency below threshold bank 1 (11/22)

Freeze Frame:


Fuel SYS1 CL

Fuel SYS2 N/A

Load PCT 92,2

ETC (F) 221

ShrtFT1 (%) 2.3

Long FT1 % -3.1

Map kpa 27.8

Rpm (min) 1903

VSS (mph) 52

IAT 54

I should add that the car runs fine.

Fuel SYS 1 CL = Fuel injector bank 1 is in the Closed Loop mode.

Fuel SYS 2 N/A = There is no fuel injector bank 2. So it must be an inline 4/6 cylinder engine.

Load PCT 92.2 = The amount of air volume entering the engine below 100%

ECT (F) 221 = Engine coolant temperature.

ShrtFT 1(%)2.3 = The O2 sensor is adjusting the fuel injectors under short term fuel trim at 2.3%

Long FT1 (%) -3.1 = The O2 sensor hasn’t yet switch over to the long term fuel trim for the injectors.

Map kpa 27.8 = The Manifold Absolute Pressure sensor is receiving a pressure signal of 27.8 kilopascals.

Rpm (min) = Engine RPM’s at the time data was recorded.

VSS (mph)52 = Vehicle speed when data was recorded.

IAT 54 = Intake Air Temperature in degrees F.


Thanks very much tester for doing that. I guess my ultimate single question is do those numbers sound within parameters? Are they supposed to help indicate a well-running engine, or help shed light on the error engine light PO 420 catalyst system efficiency below threshold bank 1 code?

Thanks again.

This code has no bearing on the running of the engine, just an emissions check to see if the catalytic converter is functioning properly. The code is set when the secondary O2 sensor (after the cat) is reading similarly to the primary O2 sensor (in front of the cat). When this happens, the ECM is assuming the cat is not functioning properly, and will set the code P0420.

Tanks BK. So–and forgive my extreme ignorance–I assume the relevent readings here are the Short FT 1 and Long FT1–could you or a tech tell from those readings that the cat is not functioning correctly? or is it just that at some point other than when this data was recorded there was a malfunction which triggered the check engine light? I ask because the instructions on the ET-80 remind owners to record the data before erasing the codes so the repair tech could ascertain them.


The freeze frame data is set when the trouble code is set. The fuel trims won’t indicate the health of the catalytic converter. They will indicate if the engine is running rich or lean. You want to record the freeze frame data because it can contain information which MAY help you in a solution to the problem.
The code P0420 for, “catalytic converter (cc)efficiency too low”, is from the comparison of the signals from the front (of the cc) oxygen sensor to the signals from the rear (of the cc). The oxygen, in the exhaust gases at the front of the cc, should be combine with any unburned fuel in the cc on its way through the cc. At the rear of the cc, the rear oxygen sensor should not have any oxygen to measure. When it does, the oxygen didn’t combine (through catalytic action) with any fuel when going through the cc. Therefore, the cc isn’t catalyzing as it should, and is “below efficiency”.
Wait! It gets a little complicated. If the oxygen sensor(s) is (aren’t) reading correctly, code P0420 may be set erroneously. How to tell? A gas analyser could read the exhaust gases at the tail pipe; or, the signals from the oxygen sensors could be observed and evaluated. This is when it gets a little complicated.

I’m not an expert on this, but I think what you need is not the freeze frame data, but the readings over a few seconds at the downstream (rear) O2 sensor. What’s supposed to happen is that the computer continuously adjusts the amount of Oxygen in the fuel mix. You should see these variations at the upstream O2 sensor. But if the catalytic converter is working properly, they will not be seen (be much reduced?) at the downstream sensor.

I’m pretty sure that some expensive OBD2 readers as well as some of the inexpensive computer based ones can monitor the O2 sensors in real time. Or you can find the signal wire in the wiring harness, push a pin into it, and watch the signal on an analog (not digital) voltmeter. Whether you can tell anything when you see the signal is a different question.

There are some pictures with this article that may clarify things a bit.

Good luck with this. My daughters car has this same problem, every time I reset the CEL. the car goes anywhere from 2 weeks to a month before it reappears. I’ve seen quite a few posts here about this code where people have spent $ thousands and not fixed it. In fact no one has posted back that has solved it. I don’t want to follow that path so if I figure it out, I promise to post back.

I am beginning to think that it is an intermittent problem in most cases. I’ve worked through all the connectors and sensors, I’m going to look at grounds next. I am suspicious of the terminal on the negative battery cable, there is a lot of corrosion where the terminal is crimped to the wire. The terminal itself is clean but you can’t uncrimp the terminal to clean the wire itself. I’m going to put a new cable on and see if that helps.

A better cat. test is a simple test that measures the inlet and outlet temps on the cat,they should differ by about 100F if all is working well.

Oldschool has a very good idea which I’m sure he has applied numerous times. I wonder if it would apply if the engine were running very rich or very lean. Oldschool, your thoughts?

For this paticular case we have only short term correction and it is in % rather than counts. I believe there are 144 counts above 14.7 and 144 below so I dont think we can conclude this car is running so bad its out of its correction range.

But in general testing a cat for efficency when you have a situation that sets either a too lean or too rich code is probably putting the cart before the horse. Correct the too lean or too rich then test the inlet and outlet temps.

It looks like the problem is the catalytic converter because you have no O2 sensor codes. Long term fuel injector trim would only be happening if you were not accelerating when the MIL came on. That was guesswork, of course.

I noticed that your speed was 52 MPH when the MIL came on. What was the speed limit on that road. What speed do you usually drive on that road? Answer those questions and you will know if short or long term fuel injector trim is something to consider. No, it shouldn’t have anything to do with your P0420 code.

Oxygen sensors are cheaper than catalytic converters, so there is a possible starting point. The only problem with replacing it is that you don’t have any O2 sensor codes.

If you cleared the code and waited for it to come back, the freeze frame data could be completely different. That data just tells you what the readings were at the time the code was set. I would need some more training to be able to tell you.

Your car is old enough to need a new upstream oxygen sensor. So bring your VIN to the dealer to make sure you get the correct O2 sensor. Since you have a Toyota and the dealer price may be too high, you might call some parts stores first.

All the car has to do is provide you with transportation. That’s it’s job. If it’s doing that in a reasonable manner, why waste your time and money worrying about this stuff?? Do you CARE that your converter MIGHT be operating at low efficiency?? Are you willing to spend $400 or more in the hopes that CEL MIGHT say off??

I agree with Caddyman; however it will come to bear with the annual inspection next October unless I can time things right so I zero out the codes but can build up enough miles after that to satisfy the readiness monitors. Month ago I finally solved a PO 301 with new injectors. Separate issue they had to replace the small muffler towards the front of the car since a weld had come loose. The guy had a very old blade in his sawzall and it took him forever to cut the old pipe out; I was wondering if all that vibration–and if he didn’t carefully clean out the pipes before installing the new muffler could have dirties or damaged the O2 sensors.

Thanks to all.