Codes P0410/PO420

SBLAY71

MEMBER
2000 BUICK CENTURY
3.1L
6 CYL
2WD
AUTOMATIC
150,000 MILES

I have 2 trouble codes P0410 and P0420. I’m pretty handy and fix all my car issues my self. I recently replaced a new fuel pump and sending unit, crank shaft sensor and harmonic balancer, fuel filter, fuel pressure regulator, purge solenoid, upstream oxygen sensor and a few coil packs last year. When the coils were bad I didn’t get a trouble code and now I’m in awe what to do next.

But this one has me stumped.
The car has a hard start in the morning 2-3 tries and cycling the key 3 times before starting mostly in the cold morning. I have also checked power to air pump which also comes on but not sure if it is bad cause I think it is more noticeable than before. I also ran power to the switch at the canister which also clicks.

After the car starts it seems as there’s a clog in the exhaust. Car does drive normal until you stomp on it then it hesitate like crazy and sometimes I will get a backfire.

The air pump hoses were also checked for blockage along with the EGR valve it I’m not sure the pump is blowing air hard enough or how much it’s supposed to blow. I don’t want to replace the pump but I’m thinking it might be the problem and the P0420 might go away.

Hoping you can give some good advise.

You guys are great.

-Scott

1 Reply

ASEMASTER6371

MECHANIC
52,797 POSTS

Good afternoon,

The 420 is a cat efficiency code. The precious metals are worn out. The cat needs to be replaced.

As far as the 410, I posted the description below. You will need a scan tool to see if the system is working correctly.

As far as the hard start, what is the fuel pressure when cold? I know you replaced it but you need to verify proper pressure.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Roy

CIRCUIT DESCRIPTION
An AIR pump is used on this vehicle to lower tail pipe emissions on start-up. The PCM grounds the AIR pump Relay control circuit, which energizes the AIR pump. The PCM also grounds the AIR combination valve vacuum (Injection Pump Bypass Valve Solenoid) control circuit, which energizes the AIR vacuum solenoid valve (Injection Pump Bypass Valve Solenoid). Vacuum is then applied to both AIR combination valve (Check Valves) diaphragms which open the shut off valves. The PCM enables both circuits simultaneously when AIR system operation is desired. When the AIR system is active, the AIR pump forces fresh air into the exhaust stream in order to accelerate catalyst operation. When the AIR system is inactive the shut off valves prevent air flow in either direction. DTC P0412 applies to the AIR vacuum control solenoid circuit. DTC P0418 applies to the AIR pump relay control circuit. DTC P0410 sets if an air flow problem is detected.

The PCM will run up to 3 diagnostic tests using the HO2S1 voltage to diagnose the AIR system. The first test is a passive test with 2 parts. The 2 parts are the AIR Passive Test 1 and AIR Passive Test 2. The second test is an active test with one part. This test is named AIR Active Test.

The AIR Passive/Active Tests consist of the following:

AIR Passive Test 1
When the AIR system is enabled, the PCM monitors the HO2S 1 voltage for a specific amount of time calculated by the coolant temperature at start-up. The HO2S 1 is monitored for 10 seconds if the coolant temperature is above 90°C (194°F), or 70 seconds if the coolant temperature is below 90°C (194°F).
If the HO2S 1 voltage goes below a calibrated amount, the PCM interprets this as an indication the AIR System is operational and considers the test passed.
When the AIR Passive Test 1 completes, the PCM then runs the AIR Passive Test 2.

AIR Passive Test 2
When the AIR System is disabled, the PCM monitors the HO2S 1 voltage. The HO2S 1 voltage should increase above a calibrated amount and switch normally.
When the AIR Passive Test 2 is complete and both AIR Passive tests indicate a pass, further action is not taken. If either one of the above tests have failed or is inconclusive, the diagnostic will proceed to the AIR Active Test.

AIR Active Test
During this test the PCM turns the AIR system on during closed loop operation. When the AIR system is activated, the PCM monitors the HO2S voltage. If the AIR system is operating properly, the HO2S 1 voltage should go below a predetermined level.
The PCM will repeat this test up to 3 consecutive times with a short delay between each command.
If the PCM determines that the HO2S 1 voltage did not respond as expected during the tests, DTC P0410 will set.

CONDITIONS FOR RUNNING THE DTC
DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0171, P0172, P0300, P0412, P0418, P0442, P0443, P1441 and HO2S DTCs are not set.
The engine operates for more than 2 seconds.

CONDITION FOR NOT PASSING AIR ACTIVE TEST
The HO2S 1 voltage changes less than 0.06 V or is above 225 mV for 1.5 seconds during 2.5 seconds of AIR pump operation.

CONDITIONS FOR SETTING THE DTC
If the AIR system fails 3 consecutive tests.

ACTION TAKEN WHEN THE DTC SETS
The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

CONDITIONS FOR CLEARING THE MIL/DTC
The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS
Inspect for the following:

NOTE: Refer to Continuous Operation of the Air Pump Notice in Service Precautions.

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

Poor terminal connection-Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension.
Damaged harness-Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault.
PCM and engine grounds for clean and secure connections

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table:
2. DTC P0412 AIR Solenoid Valve Control Circuit and P0418 AIR Pump Relay Control Circuit should be diagnosed first if either are set.
3. Begins testing for a short to ground in the AIR pump feed circuit.
4. Listen for a running motor. Command both the ON and OFF states. Repeat the commands as necessary.
5. Begins testing for a short to voltage in the pump feed circuit.
6. Tests for voltage at the AIR pump relay switch feed circuit.
7. Bypasses the relay.
8. Tests for voltage on the AIR pump feed circuit.
9. Tests for an open on the pump ground circuit.
28. The AIR Pump is not designed to run continuously. If the pump needs to be replaced, inspect for conditions that may cause continuous pump operation.