every now and then my SES light will come on for a few days then shut off for a for a month or so then come back again, i hooked up and obd 2 scan tool to my car and scan for codes it had a record of a code P0420 which it said was a "low catalyst efficiency bank 1", does this mean one of my cats is bad or that my o2 sensors are malfunctioning? or is it something else? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> the only mods i have to my car are a lid and corsa catback, but i couldnt see either of these causing a trouble code for the catalytic converters. any info would be greatly appreciated, thanks

 

I am a GM technician and in my experiences the P0420 code for catalyst low efficiecy has always resulted in a malfuctioning converter. This is the only reason this code will set. If the sensors aren't functioning properly, there are several other codes that will set for them. You need a new cat.

 

What car do you have and what is the mileage. There is a good chance the converter will be covered under factory warranty.

 

sorry it took a couple of days to reply, i was busy this weekend working on my house, i have a 2001 m6 trans am, i have the 3/36000 mile warranty on it and i believe all emmissions equipment is also warrantied for 5 or 7 years, am i right in assumming this? if so i should be able to have gm replace the cat for free? thanks for your help on this

 

Unfortunately I am having problems accessing SI2000 right now, but per the Government, any emission related device has to be warrantied by them for 5 years/75,000 miles if memory serves me correct.

Either way, it'll be covered if that is the problem.

I'd like to get the troubleshooting list before taking a random stab and the dark and saying "Yea, it's the cat!"

 

i have very little knowledge of computer cars,this is my second car before this i had a 73 mustang that i rebuilt, which was a lot simpler to diagnose problems. At my college we have a obd2 scan tool so the only way i could say i troubleshooted the problem was i hooked up the tool and scan the memory for stored codes and the P0420 came up and it was stored in the memory 8 times, a member on this site told me to switch the o2 sensors around to check them and if the P0420 code still comes up its the cat, the only other question i have is "bank 1" the drivers or passenger's side cat? thanks for the help <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

 

Bank one is the Drivers side. You could try switching the O2 sensors, but its probably the cat.

 

thanks man, im probably just gonna bring the car in to get it looked at, theres no need to for me to crawl underneath the car a switch the o2 sensors, its still under warranty

 

Yep, that's what I'd do. Less headaches for you. And as long as it's under warranty...

 

After you've tried all the ideas that have already been suggested you can also gut your cats and install O2 Simms or buy LS1 Edit and DELETE the post cat O2s which assumes you've either gutted the cats or eliminated them altogether. If you've got deep pockets try the latter.

 

Woohoo, I'm back into SI

Here ya go;

P0420
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">DTC P0420 Catalyst System Low Efficiency Bank 1

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 condition 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 Running 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.
- The ECT is greater than 65°C (149°F).
- The vehicle speed is between 32 km/h (20 mph) and 136 km/h (85 mph).
- The IAT is greater than -30°C (-22°F).
- The TP sensor angle is greater than 2%.
- The engine speed is between 800 RPM and 3000 RPM.
- The MAP is between 25 kPa and 80 kPa.
- The engine air flow is between 14 g/s and 40 g/s.
- The fuel system is operating in closed loop fuel control.

Conditions for Setting the DTC

The PCM determines the 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 Description

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

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

Step 1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?
--
Yes: Go to Step 2
No: Go to Powertrain On Board Diagnostic (OBD) System Check

Step 2

Are any other DTCs set?
--
Yes: Go to the applicable DTC table
No: Go to Step 3

Step 3

Inspect 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.).
- Ensure 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).
- Ensure 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?
--
Yes: Go to Step 5
No: Go to Step 4

Step 4

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

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

Step 5

1) Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool.
2) Idle the engine at the normal operating temperature.
3) Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool.
4) Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test ran and passed?
--
Yes: Go to Step 6
No: Go to Step 2

Step 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?
--
Yes: Go to the applicable DTC table
No: System OK</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">