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Discussion Starter #1
I have a 2007 Chevy Cobalt 2.2L and the check engine light came on some time ago. A mechanic scanned it and said no big deal until I need to get it smogged. Now, I need to get it smogged. I've taken it to several mechanics who have not been able to fix it, so I'm asking for your experienced advice.

The codes were P0102, P0121, P2431, and P2433. The mechanic found a hose connectd to the air duct that was loose, so $350 to replace the entire duct and the CEL came right back on. I drove it home and it was down to 3 codes. I cleaned the MAF sensor and it went down to one, but after driving and starting the car again, CEL comes back on. I've already replaced the air filter and checked all of the fuses. The mechanic cleaned the throttle body when replacing the air duct.

So, now, the only code is P2433 (secondary air injection system pressure sensor circuit high voltage bank 1). What can I check myself and what can I ask a mechanic to check on this?

Thanks in advance!
 

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DTC P2430-P2433

Circuit/System Description
The secondary air injection (AIR) system aids in the reduction of hydrocarbon emissions during a cold start. The system forces fresh filtered air into the exhaust stream in order to accelerate the catalyst operation. An electric air pump, the secondary AIR injection pump, provides filtered air on demand to the AIR control solenoid valve/pressure sensor assembly. The AIR control solenoid valve/pressure sensor assembly controls the flow of air from the AIR pump to the exhaust manifold. The AIR solenoid relay supplies the current needed to operate the AIR control solenoid valve/pressure sensor assembly. A pressure sensor is used to monitor the air flow from the AIR pump. The engine control module (ECM) supplies the internal pressure sensor with a 5-volt reference, an electrical ground, and a signal circuit.

Circuit/System Testing
Important: The Circuit/System Verification must be performed first or misdiagnosis may result.

Ignition OFF, disconnect the harness connector at the AIR solenoid valve.
Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit terminal 1 and ground.
If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the control module.
Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 3 and ground.
If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the control module.
If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the control module.
Verify the scan tool AIR Pressure Sensor parameter is less than 0.5 volts.
If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the control module.
Install a 3A fused jumper wire between the signal circuit terminal 2 and the 5-volt reference circuit terminal 3. Verify the scan tool AIR Pressure Sensor parameter is greater than 4.9 volts.
If less than the specified range, test the signal circuit for short to ground or an open/high resistance. If the circuit tests normal, replace the control module.
Connect all electrical connectors.
Ignition ON, engine OFF, observe the AIR Pressure Sensor parameter.
If the AIR Pressure Sensor parameter does not equal the BARO parameter, replace the AIR solenoid valve.
Engine RUNNING, enable the AIR solenoid valve with a scan tool and observe that the AIR Pressure Sensor parameter equals approximately 8-10 kPa above BARO.
If not within the specified range, continue with this procedure.
Remove the AIR inlet hose from the AIR pump.
Engine RUNNING, enable the AIR solenoid valve with a scan tool and observe that the AIR Pressure Sensor parameter increases to 8-10 kPa above BARO.
If within the specified range, the AIR pump inlet hoses/pipes are restricted. Remove the restriction or replace the hose/pipe.
If not within the specified range, continue with this procedure.
Disconnect the hose from the AIR pump outlet.
Disconnect the hose quick-connect from the AIR solenoid valve inlet.
Install a length of standard 1 inch I.D. (25.4 mm) hose from the AIR pump outlet to the AIR solenoid valve inlet.
Engine RUNNING, enable the AIR solenoid valve with a scan tool and observe that the AIR Pressure Sensor parameter increases to 8-10 kPa above BARO.
If within the specified range, the AIR pump outlet hoses/pipes are restricted or leaking. Remove the restriction or replace the hose/pipe.
If less than the specified range, replace the AIR pump.
If more than the specified range, continue with this procedure.
Remove the AIR solenoid valve.
Leave the standard hose and harness connector connected.
Engine RUNNING, enable the AIR solenoid valve with a scan tool and observe that the AIR Pressure Sensor parameter increases to approximately 7 kPa above BARO.
If more than the specified range, replace the AIR solenoid valve.
If within the specified range, test/inspect the cylinder head for restriction.
 

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Discussion Starter #3
Ah, that's too complicated for me, but I'll print it out and take it to the mechanic. I know how to do some of that stuff, but there are just things that I don't understand. I know how to measure the resistance of a component, but I don't know what things like, "the low reference circuit terminal 1" or "5-volt reference circuit" are.

Thanks for the thorough response.

scitch
 

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I know, some stuff is better left to the professionals with the proper tools and skills. Sometimes by avoiding more damage it is less costly.
 
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