PO420 weak catalyst

Hi folks,

Had the oil changed in the wife's Escort last weekend. (Thought I'd try letting somebody else do it. Big mistake.) Within a day the check engine light came on and engine runs rough. Had the codes checked and am getting PO420 weak catalyst. This points to catalytic converter, but isn't there two and a sensor on one of them? I'm wondering if somebody broke a wire.

Thanks
Bill

Forgot to post the model year and engine 1.9, 1996.

Well that is a old clasic about the last person that worked on it done it.
BUT BEFORE YOU BLAIM THEM CHECK IT OUT.
If a wire was off it should set a 02 sensor code.
A code 420 does not say the cat is bad it says check it out.
Many things can cause a 420-430 code.
Start with checking your tune up end and fuel and computer system.
Here is a link on checking codes 420/430
http://www.troublecodes.net/articles/catfailure/

MT

Hi folks,

Had the oil changed in the wife's Escort last weekend. (Thought I'd try letting somebody else do it. Big mistake.) Within a day the check engine light came on and engine runs rough. Had the codes checked and am getting PO420 weak catalyst. This points to catalytic converter, but isn't there two and a sensor on one of them? I'm wondering if somebody broke a wire.

Thanks
Bill

There is only 1 Catalytic converter and the sensor is in the inlet pipe of the converter. Check it to see if the wire has come loose. There's a harness about 12 inches from the HEGO (Heated Exhaust Gas Oxygen) sensor.
The inlet pipe is just downstream from the exhaust manifold. Since you have the OBD 11 there may be a second oxygen sensor on the downsteam side of the catalytic converter which can be acessed from underneath the car.

They may be looking for some return business. Naw, they wouldn't do that... :grinyes:

Davescort97
There is no way a car can set a cat code with only one 02 sensor.
Unless the front sensor has figured a way to jump back back behind the cat every few seconds and read the exhust in front and rear at the same time.
Also on OBD11 pcm you need a scanner to clear the code. They have a memory like a elephant. A battery disconnect does not erase there memeory.
Also a battery disconnect is dangerous to there health.
:grinyes: :grinno: :lol2:
MT

If the shop did anything wrong then I'd think the engine light would have come on as soon as you left.

Just out of curiosity, does this shop do exhaust work too? :confused:

Wally World did the oil change while we were shopping. I noticed a sputtering/bucking feel when we got it back. Next day wife said the check engine light came on next day. Seems like a strange coincidence that the problems started after they did the work.

Check the HEGO sensor wiring and it's OK. I changed the sensor not too long ago. I figure a vacuum hose got knocked off, like maybe to the EGR valve controls. But have yet to find it. Is there another sensor past the HEGO?

On my '93 there's nothing past the HEGO that I know of. I guess if they checked the air filter at Wal-Mart then they may have unhooked the Charge air Temp Sensor or Mass Air Flow Sensor.

Thanks for the info. I went ahead and did the old battery disconnect PCM reset. Left it disconnected for a couple of hours. After that, no more check engine and it runs better. Hmmm.

OK folks. The code came back and I took it to an exhaust shop to see what the owner could tell me. He tells me the converters on the Escorts that are built into the exhaust mainfold (what si on my car) rarely go bad. He suggested checking the second O2 sensor. I know this was tossed around earlier, but do these cars have up and down stream sensors?

Thanks

OK folks. The code came back and I took it to an exhaust shop to see what the owner could tell me. He tells me the converters on the Escorts that are built into the exhaust mainfold (what si on my car) rarely go bad. He suggested checking the second O2 sensor. I know this was tossed around earlier, but do these cars have up and down stream sensors?

Thanks

Found the down stream sensor! It is just ahead of the mid-pipe and full of some gooey carbon type stuff. :)

Are you sure it is the same code that came back?
The first thing would be to check you tune up end.
A engine not running right,missfire or engine running rich can cause cat codes.
A weak front 02 sensor would come more setting the code that the back sensor.
The 96 escort 1.9 has a front and reat 02 sensor.
The code sets when the pcm does not see any differance from the front to rear 02 sensor readings or the cat is dead not doing anything.
If you can get it on a good engine scanner you can watch the front and rear 02 sensors readings. If the front is lower than the rear the front 02 sensor is weak . If they are the same the cat is weak or the front o2 sensor is weak.
Here is a link on checking for that code.
http://www.troublecodes.net/articles/catfailure/
Also some info on that code.
DTC P0420, P0421, P0430 & P0431: Check Possible Cause Of Misfire DTC P0420 and P0421 indicates bank one catalyst system efficiency is minimum requirement. DTC P0430 and P0430 indicates bank 2 catalyst system efficiency is minimum requirement. Possible causes are as follows: Use of leaded fuel. Oil contamination. Cylinder misfire. Fuel pressure too high. HO2S sensor improperly connected. Damaged exhaust system component. Faulty ECT sensor. Faulty HO2S. Ensure ignition timing is correct. Retrieve all Continuous Memory DTCs. If misfire code(s) is not present, go to next step. If misfire code(s) is present, isolate cylinder and repair as necessary. Check HO2S Monitor DTCs If DTCs P0136, P0138, P0140, P0141, P0156, P0158, P0160, or P0161 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. Check ECT Sensor DTCs If DTCs P0117, P0118, P0125 or P1117 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. If any codes except P0420, P0421, P0430 and/or P0430 were present in step 1), service as necessary before continuing. If no codes except P0420 and/or P0430 were present in step 1), go to next step. Check Rear HO2S Wiring Harness Turn ignition off. Ensure HO2S wiring harness is correctly routed and connectors are tight. Repair or replace as necessary. If wiring harness and connectors are okay, go to next step. Check Fuel Pressure Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST HC . Check For Exhaust System Leaks If exhaust system leaks, it may cause catalyst monitor efficiency test to fail. Inspect exhaust system for cracks, loose connections or punctures. Repair or replace as necessary. If exhaust system is okay, go to next step. Check For Exhaust System Restrictions Inspect exhaust system for collapsed areas, dents or excessive bending. Repair or replace as necessary. If exhaust system is okay, go to next step. Ć Check Manifold Vacuum Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Start engine and raise engine speed to 2000 RPM. Manifold vacuum should rise to more than 16 in. Hg. If manifold vacuum is okay, go to next step. If manifold vacuum is low, go to step 11). Leave tachometer and vacuum gauge connected. Start engine and raise engine speed to 2000 RPM. On a non- restricted system, manifold vacuum should quickly rise to normal range as increased RPM is maintained. On a restricted system, manifold vacuum will slowly rise to normal range as increased RPM is maintained. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If manifold vacuum is low or slow to respond, go to next step. Leave tachometer and vacuum gauge connected. Remove exhaust pipe from exhaust manifold. Start engineand raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is downstream from exhaust manifold. Reconnect exhaust pipe to exhaust manifold and go to next step. If manifold vacuum is still low or slow to respond, fault is in exhaust manifold or intake manifold gasket. Repair or replace as necessary and repeat QUICK TEST. Leave tachometer and vacuum gauge connected. Disconnect muffler/tailpipe assembly from rear of catalytic converter. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is in muffler/tailpipe assembly. Repair or replace as necessary and test drive vehicle to verify elimination of symptom. If manifold vacuum is still not okay, fault is in catalytic converter. Repair or replace as necessary. Check tailpipe/muffler assembly for debris from catalytic converter. Test drive vehicle to verify elimination of symptom.
Good Luck MT. :lol: :grinyes:

Is that a wet carbon or dry. You might pull the front on out to and have a look at it also .
If it is a wet glooey stuff post back
If front and rear are the same and you are going to replace one replace the front one with the new sensor and move the front to rear or clean rear with carb cleaner.
MT

I believe the carbon was dry. I used some Kryoil on the threads to get it loose and there was some wetness in that area. Further away from the threads it was dry and as I got toward the tip where the holes are the coating was brownish/white like plugs get some times.

I cleaned that lower O2 with the carb cleaner and brush. Did a test drive and it seems to run better. I know the hesitation that was there is gone. Still running a little rough though. So, I'll probably pull the upper O2 and plugs and look at them after it cools. I just replaced that upper sensor a couple months back. So, I hope it's not bad.

Thanks

Well, the code raised it's ugly head again today.

I'm testing what hasn't already been replaced. With regard to the upstream or hot O2 sensor, when I test resistance across the four terminals I get nothing not matter which combination I test. Isn't there supposed to be some sort of resistance across the heater?

And, the converter on these cars runs from the exhaust manifold to the mid pipe connection and has both O2 sensors mounted to it. Right? The reason I ask is a local exhaust shop told me the manifold and converter are one cast piece.

Thanks

To follow up the last post, I'm wondering if the other driver (read wife), I used to drive a 2000 Ranger daily until a couple weeks ago, hit something with the catalytic converter. There is a local railroad crossing we use frequently and it would be real easy to bottom out while crossing it.

Well, the code raised it's ugly head again today.

I'm testing what hasn't already been replaced. With regard to the upstream or hot O2 sensor, when I test resistance across the four terminals I get nothing not matter which combination I test. Isn't there supposed to be some sort of resistance across the heater?

And, the converter on these cars runs from the exhaust manifold to the mid pipe connection and has both O2 sensors mounted to it. Right? The reason I ask is a local exhaust shop told me the manifold and converter are one cast piece.

Thanks

I can not find any specs on testing it but you should have at least have 4-5 ohms On the heater circuit part.
Get a new 02 sensor and test it and see what it has.
Are you using OEM 02 sensors or them splice in jobs?
What was the code no that returned?

The sensor is a Bosch oem replacement. I'll see if somebody will let me test one.

The code is P0420.

Thanks

i have the same problem with my '96 lx. the check engine light is on, even flashes on and off sometimes, and the car sputters every once in a while. had it scanned and also got the p0420 code. could be a trend in these cars.

I ended up replacing both O2's, and the ECT, along with DPFE sensor and EGR solenoid. The downstream O2 and EGR stuff had 174K on them and tested OK, but were marginal. I also figure with that many miles they were due.

Also, got to talking with a guy at an Autozone who told me a lot of the weak catalyst codes started popping up after Katrina. His son had the problem and changed brands and grades of gasoline, which corrected the problem.