I am getting an intermittent P0430 code. The manuals say it involves O2 sensor readings (voltage differences etc). Is this normally an indication of a Sensor failing or a CAT Failing? 2002 Coupe A4 89,000 Miles.

Thanks

Phil

 

Here is the diagnostic procedure for that code. Other than a wiring problem the CAT is the major suspect. Depending on age and mileage the CAT may be covered under the emissions warranty.

Bill

DTC P0420 or P0430
Circuit Description
In order to maintain low emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), the engine controls system uses a 3-way catalytic converter. The catalyst within the converter promotes a chemical reaction, which oxidizes the HC and CO that are present in the exhaust gas. This reaction converts these chemicals into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting NOx into nitrogen. The powertrain control module (PCM) monitors this process using heated oxygen sensor (HO2S) bank 1 sensor 2. HO2S bank 1 sensor 2, located in the exhaust stream past the 3-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalyst's ability to effectively convert the exhaust emissions. If the catalyst is functioning correctly, the HO2S bank 1 sensor 2 signal will be far less active than the signal that is produced by HO2S bank 1 sensor 1. This indicates that the 3-way catalytic converter's oxygen storage capacity is below an acceptable threshold.

The PCM performs this diagnostic during idle. When the conditions for running this DTC are met, the following conditions occurs:

The PCM captures the current rear HO2S rich-to-lean status.
The air-to-fuel ratio transitions from rich to lean or from lean to rich, depending on the capture rear HO2S rich-to-lean status.
The air-to-fuel ratio transitions a second time opposite the first air-to-fuel ratio transition.
The PCM captures the response time of the front and rear heated oxygen sensors when the air-to-fuel ratio transitions occur. The HO2S response time goes from less 300 mV to more than 600 mV, and from more than 600 mV to less than 300 mV.
The PCM measures the time it takes the rear HO2S voltage to cross a reference rich-to-lean threshold, minus the time it takes the front HO2S voltage to cross the same rich-to-lean threshold. The difference between the front HO2S time and the rear HO2S time is the oxygen storage capacity of the catalyst. This DTC sets if the time exceeds a predetermined threshold.
Conditions for Running the DTC
DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0131, P0133, P0134, P0135, P0137, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0171, P0172, P0174, P0175, P0200, P0300, P0335, P0336, P0341, P0342, P0343, P0351-P0358, P0410, P0440, P0502, P0503, P0506, P0507, P0606, P1120, P1133, P1134, P1153, P1154, P1220, P1336, P1415, P1416, or P1441 are not set.
The intake air temperature (IAT) is more than -7°C (19°F), but less than 75°C (167°F).
The barometric pressure (BARO) is more than 74 kPa (10.7 psi).
The engine is operating.
The engine coolant temperature (ECT) is more than 75°C (167°F), but less than 117°C (243°F).
Since the end of the last idle period, the engine speed is more than 850 RPM for a minimum of:
17 seconds for manual transmissions
27 seconds for automatic transmissions
The Closed Loop fuel control is enabled.
Conditions for Setting the DTC
The PCM determines if oxygen storage capability of the catalytic converter has degraded to less than a calibrated threshold.

Action Taken When the DTC Sets
The malfunction indicator lamp (MIL) is turned ON.
A DTC is stored in memory.
The Freeze Frame/Failure Records are stored.
The Failure Records are updated after the first failure of each ignition cycle.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Test Description
The number below refers to the step number on the diagnostic table.

Before you replace the 3-way catalytic converter, correct any conditions which may have damaged the catalyst.

Step
Action
Yes
No

1
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls

2
Are any other DTCs set?
Go to the applicable DTC table
Go to Step 3

3
Check for the following conditions:

Verify that the 3-way catalytic converter is an original equipment part.
Inspect the 3-way catalytic converter for damage from the following conditions:
Dents
Severe discoloration caused by excessive temperatures
Holes
Other conditions
Ensure that an internal 3-way catalytic converter rattle that is caused by a damaged catalyst is not present.
Inspect the exhaust system for the following conditions:
Leaks
Damage
Loose hardware
Missing hardware
Ensure that the HO2S 1 and the HO2S 2 are secure, and ensure that the pigtails and the wiring are not damaged or contacting the exhaust.
Did you find and correct the condition?
Go to Step 5
Go to Step 4

4
Replace the catalytic converter. Refer to Catalytic Converter Replacement in Engine Exhaust.

Is the action complete?
Go to Step 5
--

5
Use a scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass?
Go to Step 6
Go to Step 2

6
With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?
Go to Diagnostic Trouble Code (DTC) List
System OK

 

Thanks for the reply and info.

Problem appears to have gone away. Hopefully stays that way, but since I have said that.......


Phil

 

Wow, thanks Bill! Great info. I threw codes P0133 & P1133 today and just reset them. I had the rears sensors deleted in a tune when I added LT headers and hi-flo cats recently, so I'll check the wires and for any leaks.

Thanks again for the great post, this forum does have it's moments.

Makes me feel all warm and fuzzy.

 

Following up here, in case someone does a search for this in the future. I couldn't find any leak or fried wires so I emailed Darrell at Xtreme. My codes ended up being thrown by a bad O2 sensor. Shoulda just bought new ones when I put the headers in, ...but I’m a chronic cheapskate. Duh.
Anyway, my sincere thanks to Dave, Darrell, and the crew at Xtreme, http://www.xmsengineering.com/home/. They got me in and out with no notice, as well as endured my endless questions and snooping around their shop. Dave also took the time to b.s. with me about ‘vettes and Mopars. I was snoopin’ around this black Hemi Charger getting serious mods in the shop, come to find out it’s his test mule. Offered to let me test drive it when it’s back in one piece. Sign me up!

 

The intermittent 0430 Code is back , but usually only occurs once per drive. Always happens after 20 minute (or so) freeway run and then only after slowing down in street traffic for a few minutes. I reset the code and it's gone. Sometimes happens once on way to work in am and almost always again on way home in the afternoon.

Weird ain't it.

Phil

 

The PCM will barf up a P0430 when it sees too much action (Oxygen) on the rear bank 2 (passenger side) oxygen sensor. As has been mentioned many times here the rear 02 sensors are for monitoring the catalytic converters. A P0430 is not usually a problem with the sensor but rather a cat or cat’s. A good cat will use almost all of the available 02 trying to kill any CO – HC and Nox that made its way past the exhaust valves. If the exhaust is stock time to talk to Chevy. For most cars cats are warranted 10 years or 100,000 miles. I see you also live in CA so you’ll have to deal with this before your next smog test. Good luck.

 

if you have lt headers with high flow cats and if the rear o2's are good, o2 sims should solve your problem.