I had my FI car tuned with stock mani's and no cats. I came home an put long tube headers with cars on the car now I am throwing codes and check engine light comes one. Is this caused by the cats?

 

 

Check your codes and see if you have P0430 or P0420. (Look in Tech Tips for instructions on how to check codes if you need that.)

I have this code sometimes with my long tubes and high flow cats. I reset and sometimes it comes back right away, other times I will go weeks without setting it.

The code is set when the PCM doesn't like the oxygen level (too high) as reported by the rear 02 sensors.

I may have bad rear 02 sensors, or I need rear O2 sims or programming to keep it from coming back.

There's a ton of information on this code in the service manual. (It's on page 6-722 in the '99 Service Manual.) Maybe someone who has an electronic copy will post it.

This code is pretty common with long tube headers and high-flow cats, but you won't hear the header vendors talking too much about it unless you ask.

 

Catalyst System Low Efficiency

Code P0420 Bank 1
Code P0430 Bank 2

Circuit Description
In order to maintain a reasonably low emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), the engine controls system uses a three-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas. This reaction converts them into harmless water vapor and Carbon Dioxide. The catalyst also reduces NOx, converting it to Nitrogen. The PCM monitors this process using Bank 1 HO2S #2. Bank 1 HO2S #2, located in the exhaust stream past the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalysts ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the Bank 1 HO2S #2 signal will be far less active than that produced by Bank 1 HO2S #1. If a problem exists which causes the PCM to detect excessive Bank 1 HO2S #2 activity outside of an acceptable range for an extended period of time, the PCM will set DTC P0420. This indicates that the three-way catalytic converters oxygen storage capacity is below a threshold considered acceptable.

Conditions for Setting the DTC
No AIR, CKP, CMP, IAT, IC, MAF, MAP, ECT, TP, EVAP, Left Bank HO2S, Misfire, Left Bank Fuel Trim, Injector, VSS, Engine Protection, or Transmission DTCs are set.
Engine is operating.
ECT is greater than 65°C (149°F).
Vehicle speed is less than 136 km/h (85 mph).
Throttle angle is greater than 10%.
Engine speed is less than 4000 RPM.
MAP is between 25 kPa and 80 kPa.
Air flow is between 14 gm/s and 40 gm/s.
Closed loop fuel control enabled.
The PCM determines oxygen storage capability of the catalytic converter has degraded below a calibrated threshold.

Action Taken When the DTC Sets
The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records.

Conditions for Clearing the MIL/DTC
The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Use a scan tool in order to clear the MIL and the DTC.
Test


Test Description
The numbers below refer to the step numbers on the diagnostic table.

Before replacing the Three Way Catalytic Converter, correct any conditions which may have damaged the catalyst.

Step
Action
Value(s)
Yes
No

1
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?
--
Go to Step 2
Go to Powertrain On Board Diagnostic (OBD) System Check

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 three-way catalytic converter is an original equipment part.
Inspect the three-way catalytic converter for damage (dents, severe discoloration caused by excessive temperature, holes, etc.).
Insure that the internal three-way catalytic converter rattle caused by damaged catalyst is not present.
Inspect the exhaust system for leaks, damage, or loose or missing hardware (area from converter to HO2S #2 primarily).
Insure that the HO2S #1 and the HO2S #2 are secure and that the pigtails and 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.

Is the action complete?
--
Go to Step 5
--

5
Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool.
Idle the engine at the normal operating temperature.
Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool.
Operate the vehicle within the Conditions for Setting the DTC as specified in the supporting text, if applicable.
Does the scan tool indicate that this test ran and passed?
--
Go to Step 6
Go to Step 2

6
Select the Capture Info option and the Review Info option using the scan tool.

Does the scan tool display any DTCs that you have not diagnosed?
--
Go to the applicable DTC table
System OK


I hope this helps.

Mike

 

I have the same problem since I got my LGM LT's installed. My codes are different though as follows:

P0133 H C
P0153 H C
P1571 H (more rare though)

Some days I get these codes several times/day. Sometimes I can go several days between codes. I just reset and move on.

 

All i can say is thank god for the O2 Sim.

Shane

 

Ive got sims