[fmcastro]

On my '06 DTS I have a P0420 after a 40 minute idling while looking at Christmas lights. Would disconnecting the battery and grounding the positive cable (to discharge the capacitors) erase the trouble code? My Cadillac dealer wants to reprogram the PCM at a cost of $144. The car runs great and gets excellent gas mileage.

 

[Submariner409]

If the P 0420 does not disappear within a week of normal start-stop-start-go driving, THEN consider having a dealer (or AutoZone) clear the SES........ or go out in the boonies and literally run the dog-snot out of the car. You won't hurt it. The Northstar is a very, very happy engine up around 5500 rpm.

IF a fault is sensed, a code sets (and maybe the SES if it's an emission code). The code remains Current for three start-run cycles during which the fault does not occur. Then the code goes to History and the light should extinguish. The code will remain as History for at least 30 start-run cycles during which the fault does not again set, when the code self-clears.

 

[Superjim]

Pretty much what Submariner409 said...
It may just need some good old fashioned HARD DRIVING...

Here is a little info on the code...
P0420 Catalyst System Efficiency Below Threshold (Bank 1)

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar.

This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

 

[danog]

For vehicles repaired under the 8 year/80,000 mile emission controller warranty, use:

FMCASTRO if you meet the above its free



#06-06-04-023:

LD8, L37 Service Engine Soon (SES) Light Illuminated or Traction Disabled Message Displayed After Extended Idle,
Multiple PCM DTCs P0171, P0174, P0420, P1516, P1682, P2101, P2176 (Reprogram PCM) - (Jul 1, 2011)

Subject:

LD8, L37 Service Engine Soon (SES) Light Illuminated or Traction Disabled Message Displayed After Extended Idle, Multiple Powertrain Control Module (PCM) Diagnostic Trouble Codes (DTCs)— P0171, P0174, P0420, P1516, P1682, P2101, P2176 (Reprogram PCM)

Models:

2006 Buick Lucerne — Built Prior to VIN Breakpoint 6U211174

2006 Cadillac DTS — Built Prior to VIN Breakpoint 6U211176

with 4.6L Northstar® V8 Engine (VINs Y, 9 —RPOs LD8, L37)

​

[HR][/HR]Condition

Some customers with vehicles built prior to the above VIN breakpoints may comment on any of the following conditions:

•	An SES light illuminated or a “Traction Disabled” message displayed after a extended idle of 30 minutes or more. After further investigation, technicians may find DTC P0171 and/or P0174.

•	An SES light illuminated . After further investigation, technicians may find DTC P0420.

•	An SES light illuminated . After further investigation, technicians may find DTC P1682 along with P1516, P2101 or P2176.

​

Correction

Reprogram the PCM with the latest TIS calibrations if the above concern is encountered. An updated PCM calibration
is now available to address this concern. This calibration, or any that follow, is designed to address this concern.
Refer to Service Programming Systems (SPS) using the appropriate Service Information (SI) procedures. This latest
calibration also contains diagnostic enhancements for the “Traction Disabled”message displayed after an extended idle.

•	If P0171 or P0174 is present, check for vacuum leaks. If vacuum leaks are present, P0171 or P0174 will continue to set.

•	If P0420 is present, refer to DTC P0420 diagnostic“Repair Verification” in SI after reprogramming to determine if the catalyst is “Good” or“Bad”. Do not replace the catalytic converter unless DTC P0420 does not pass with the new calibration.

​

The new PCM calibration is available to dealerships as part of TIS2000 incremental satellite update data version 4.0 for
2006 or later, broadcast to dealers on April 3, 2006; and on TIS CD-ROM version 4.0/2006 or later, mailed to dealers beginning
April 12, 2006. As always, make sure your Tech 2® is updated with the latest software version.
Warranty Information

For vehicles repaired under the 8 year/80,000 mile emission controller warranty, use:

J6353* Module, Powertrain Control – Engine Reprogramming with SPS 0.4 hr *This labor operation is for bulletin use only. It will not be published in the Labor Time Guide.