IF IT SAYS PCM P0420 HISTORY

DTC P0420: Catalyst System Low Efficiency Bank 1
Circuit/System Description
Important: A new converter with less than 100 miles on it may set DTC P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.
A 3-way catalytic converter (TWC) controls emissions by converting hydrocarbons (HC) and carbon monoxide (CO) into carbon dioxide (CO2), and oxides of nitrogen (NOx) into nitrogen. The TWC also stores oxygen. When the listed idle conditions follow the listed driving conditions, the Catalyst System Efficiency test will run. The powertrain control module (PCM) monitors this oxygen storage capacity by comparing the pre and post-catalyst oxygen sensor signals while adding and subtracting fuel during specific idle conditions. The PCM compares the pre and post-catalyst-oxygen sensor signals to determine if the oxygen storage capacity of the catalyst is degraded.

https://www.youtube.com/watch?v=CflIvd5VOoA&t=293s

Among these problems are stubborn OBDII error codes like P0430. The P0430 check engine light code, like P0420, means the catalyst system efficiency is below the required threshold.

When your OBD-II equipped vehicle exhibits a code P0454, it means that the powertrain control module (PCM) has detected an intermittent signal from the evaporative emissions (EVAP) system pressure sensor circuit. ... EVAP pressure is monitored by the PCM using the EVAP pressure sensor.

Don't have emission testing where you live ? Take the bulb out of the dash ! You illegal anyway !

Take it to a ASE certified repair facility ,they'll fix it up ! Don't just replace parts !!!!!

P0171 - is a lean code bank 1 -possible vacuum leak , low fuel pressure , plugged fuel filter ,
P0300 - is a random misfire code which is understandable with a lean code .
P0420 As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first
P0452 - EVAP Control System Pressure Sensor Low Input
P0446 - Evaporative Emission Vent System Performance
P0453 - Fuel Tank Pressure Sensor Circuit High Voltage
P1639 - PCM 5 Volt Reference Voltage Circuit Condition
P1653 - Power Steering Output Circuit Malfunction
P1651 - Fan 1 Relay Control Circuit
If you don't know what your doing take it to a repair shop before you waste your money ! You have a lot of problems here an I don't think the computer is bad , I'd say lack of maintenance ! You need to learn how to test thing's to fix them ! From the five volt reference voltage code , I'd say one of your sensors is shorted internally bring down the ref. voltage circuit causing the no start, but then again the 5volt ref. circuit in the PCM could be the problem . What you need to do is Disconnect all sensors that receive 5volt ref. signal one at a time an see if it will start . If I knew what year vehicle yours is I could tell you what sensors ! MAP, TPS , etc...

P0420 GMC - Catalyst System Low Efficiency Bank 1 ' Add Comment
Possible causes
- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Powertrain Control Module (PCM)
What does this mean?
Tech notes
As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first.
What does this mean?
When is the code detected?
If a condition exists which causes the Powertrain Control Module (PCM) to detect excessive Bank 1 HO2S #2 activity outside of an acceptable range for an extended period of time, the PCM will set the P0420 code. This indicates that the three-way catalytic converters oxygen storage capacity is below a threshold considered acceptable.
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P0420 GMC 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 Powertrain Control Module (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.

the history i dont need, at all.
as is true on all old cars, batteries and alts and starters a many.
so p420 has nothing to do with this , (means lazy cat, ignore it)
420 is a private hell. do not look, there, unless forced by GOV dark forces. (ask if serious, done many)

so now we have 500rpm this is clearly wrong, HOT? engine???????
this means idle controls are hosed. (bad)
bad idle means the PCM tried, to raise RPM to 800 (common)
and fail.
for 2 reasons. (and 50 causes)
1: ISC is stuck or bad.
2: engine lacks power. (too lean or misfiring are IT)
do you want to guess or test.?????????????
i can do #2 only. test.
ask.

P0420 means that 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.


Code P0351 could means thet the COP (Coil On Plug) ignition system is what is used on most modern engines. There is an individual coil for each cylinder that is controlled by the PCM (powertrain control module). It eliminates the need for spark plug wires by putting the coil right above the sparkplug. Two wires are dedicated to each coil. One is a battery feed usually from the power distribution center. The other wire is the coil driver circuit from the PCM. The PCM grounds/ungrounds this circuit to activate or deactivate the coil. The coil driver circuit is monitored by the PCM for faults.

If an open or a short is detected in the driver circuit for coil number 1, a P0351 may set. Also, depending on the vehicle, the PCM may also shut down the fuel injector to the cylinder also.

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

Hello and welcome. the code P0420 is for a bad cat. converter. replacing 02 sensors wont repair this code. the code simply's means that thje cat. converter is not working as designed and will need to be replaced.

The PCM determines the oxygen storage capability of the catalytic converter has degraded below a calibrated threshold.

IPC stands for Instrument panel control, here is a typical code repair flow chart, this is for example only and has nothing to do with your car..
P083 = 24x signal high.

P107 = Instrument panel control )IPC) to computer (PCM) data problem.

P137 = Loss of Automatic braking system (ABS) to Traction control system (TCS).

What you need to do is CLEAR all these codes from the computer and see which ones return.

Perform this test.

1. Ignition key ON. Engine OFF.

2. Simultaneously push and hold the OFF and WARMER (^) buttons on your climate control panel for 3 seconds and release them.

3. Diagnostic codes such as above will appear with the word HISTORY or CURRENT for each code.

4. The codes will stop when you see PCM?

5. Push and release the HI(^) button and you will see PCM DATA?

6. Push and release the LO(v) button and you will see PCM DATA?

7. Continue to push and release the LO (v) button until you see PCM CLEAR CODES?

8. Push and release the HI(^) button until you see PCM CODES CLEAR.

9. Turn OFF the ignition and wait 3 minutes and try and start the car. If the car starts and the light comes back ON, Turn OFF the car and repeat steps 1 thru 3 and let me know what codes you get and if they are HISTORY or CURRENT.

10. When you see PCM?, Turn OFF ignition key.

11. Let me know what codes you get and if they are HISTORY or CURRENT.



---------- FOLLOW-UP ----------

QUESTION: this is what happen when it did what you told me what to do.
P047 History,P107 History,No IPC Code, P83 History,P137 History, A047 Current, No Sir Codes, T072 History,No Russ, PCM?
ANSWER: You did not follow the directives correctly . If you had, You would NOT have any HISTORY CODES.

Try it again and follow these directives EXACTLY:

1. Ignition key ON. Engine OFF.

2. Simultaneously push and hold the OFF and WARMER (^) buttons on your climate control panel for 3 seconds and release them.

3. Diagnostic codes such as above will appear with the word HISTORY or CURRENT for each code.

4. The codes will stop when you see PCM?

5. Push and release the HI(^) button and you will see PCM DATA?

6. Push and release the LO(v) button and you will see PCM DATA?

7. Continue to push and release the LO (v) button until you see PCM CLEAR CODES?

8. Push and release the HI(^) button until you see PCM CODES CLEAR. WAIT 3 seconds and then proceed to 9.

9. Turn OFF the ignition and wait 3 minutes and try and start the car. If the car starts and the light comes back ON, Turn OFF the car and repeat steps 1 thru 3 and let me know what codes you get and if they are HISTORY or CURRENT.

10. When you see PCM?, Turn OFF ignition key.

A code P0420 may mean that one or more of the following has happened:

• Leaded fuel was used where unleaded was called for
• An oxygen sensor is not reading (functioning) properly
• The engine coolant temperature sensor is not working properly
• Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
• Retarded spark timing
• The oxygen sensors in front and behind the converter are reporting too similar of readings

A code P0131 may mean that one or more of the following has happened:

• Faulty o2 oxygen sensor
• Short to voltage on O2 signal circuit
• High resistance or open on O2 signal circuit

A code P0446 could mean one or more of the following has happened:

• Bad vacuum switch
• Broken or damaged EVAP line or canister
• Open in PCM purge command circuit
• Open or short in Voltage feed circuit to Purge Solenoid
• Faulty purge solenoid
• Restriction in EVAP solenoid, line or canister
• Corrosion or resistance in purge connector
• Bad PCM