Check Engine light-code 10PCM PO420HC
Thread Starter
Racer
Joined: Apr 2004
Posts: 373
Likes: 1
From: Grace Valley: A small, peaceful & beautiful valley in the Volunteer State
Check Engine light-code 10PCM PO420HC
Check Engine Light Stays on Steady. Only Current Code is PO420HC-Catalyst System Low Efficiency (I don’t remember this issue previously). Are there any other issues for Check Engine that don’t show up on the DIC? I’ve reviewed the manual section-“If the Light is on Steady” and checked the possible conditions, e.g. fuel cap not on tight, drive thru deep puddle of water....etc.) and have ruled them out.
As Sherlock would say “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” I don’t know if I have correctly ruled that out all the “impossible” causes and need to have the Catalyst (both?) checked out. My odometer shows 103,401miles and I’ve put the most (90+%j on over the past 15 years. The only other possibility is at about 102,000 I had my “trusted” mechanic change my plugs and wires. I specified OEM parts but I just looked at my invoice and saw that they did install ACD Plugs but they were Double Platinum-not Iridium. The check engine light came on about two days ago. Possibly a “clue?”
OF course all all ideas and suggestions are welcomE and appreciated. (I know I should have done the job myself, but the last time I did it was ~20 years ago on my ‘71 Stangj.
As Sherlock would say “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” I don’t know if I have correctly ruled that out all the “impossible” causes and need to have the Catalyst (both?) checked out. My odometer shows 103,401miles and I’ve put the most (90+%j on over the past 15 years. The only other possibility is at about 102,000 I had my “trusted” mechanic change my plugs and wires. I specified OEM parts but I just looked at my invoice and saw that they did install ACD Plugs but they were Double Platinum-not Iridium. The check engine light came on about two days ago. Possibly a “clue?”
OF course all all ideas and suggestions are welcomE and appreciated. (I know I should have done the job myself, but the last time I did it was ~20 years ago on my ‘71 Stangj.
Thread Starter
Racer
Joined: Apr 2004
Posts: 373
Likes: 1
From: Grace Valley: A small, peaceful & beautiful valley in the Volunteer State
To the best of my knowledge they are originals. I’ll go back in my records and see what I can find. But I do have to have an emissions test by the County. I can’t testify as to their accuracy, but it has been OK for the past 15 years . The test involves checking the fuel cap and a diagnostic by hooking their computer to the CPU(?) (under the dash by the steering wheel—I have to remove my window Valet before they can hook up.). I’m going to check on their site as to what they measure. I also reviewed the Maintenance Schedule and didn’t find any info about O2 sensors
Thread Starter
Racer
Joined: Apr 2004
Posts: 373
Likes: 1
From: Grace Valley: A small, peaceful & beautiful valley in the Volunteer State
To the best of my knowledge they are originals. I’ll go back in my records and see what I can find. But I do have to have an emissions test by the County. I can’t testify as to their accuracy, but it has been OK for the past 15 years . The test involves checking the fuel cap and a diagnostic by hooking their computer to the CPU(?) (under the dash by the steering wheel—I have to remove my window Valet before they can hook up.). I’m going to check on their site as to what they measure. I also reviewed the Maintenance Schedule and didn’t find any info about O2 sensors
1996-Current Gasoline Vehicles
(NOTE: the driver will need to exit the vehicle during the OBDII part of the test)
Required Tests OBDII (On Board Diagnostic) Test; Pressurized gas cap test; Visual inspection of the Catalytic Converter
Tennessee Requirements
Procedures
- The inspector will verify that the vehicle has a Catalytic Converter (if required) on the exhaust pipe (between the engine block and the muffler). If the vehicle’s catalytic converter has been removed or tampered with, the vehicle will fail the inspection
- The inspector will connect the vehicle’s gas cap to the pressurized gas cap testing equipment. The gas cap is required to hold pressure during the test.
- The inspector will connect a DLC (Data Link Connector) to the vehicle’s OBDII port (generally located under the driver’s dash). The inspector will verify that the vehicle’s MIL( Malfunction Indicator Lamp) or Check Engine light is operating correctly. The MIL is required to come on when the ignition is on and the engine is off. The MIL is then required to turn off once the engine is started.
- The inspector will instruct the computer to retrieve any diagnostic trouble codes which the vehicle’s OBD system is storing. The system is read-only and no changes to your vehicle will be made; only data related to the vehicle’s emission components will be downloaded to the emissions analyzer
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Joined: Sep 2013
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From: Cape Coral, Florida
Yo Vern !!...that's what we say in NJ !!...your plug change is in NO way related to your P0420 !!...simply put your cats have lost their ability to store oxygen...99 out of 100 times it's a cat change. P0420 is bank one...the driver's side...since you had your mechanic change your plugs and wires and I'm taking it you don't do your own maintenance have him check if the front and rear O2 sensor waveforms look identical...both switching from 150-850 mv after the cats have FULLY warmed up...if so a bad cat...if he knows how he can also do a "catalytic converter oxygen storage test" to also confirm...if he has a good scan tool and some propane he can do this test. Basically he injects propane into the engine...both upstream and downstream sensors go "rich"...he cuts off the propane and see that after about 6-10 seconds that the downstream sensors go "lean" after the upstream do...easy peezy test. Good luck but you WILL fail inspection for this !!
Last edited by C5 Diag; Sep 8, 2018 at 03:43 PM.
