My 2007 C6 with only 13,500 miles and used just for club meetings and car shows now has a check engine light. I found 4 o2 sensors on the exhaust pipes. Advance auto tech ran a scan and got these codes. #1-PO171, #2 PO174 and PO621 Gen Lamp L Control Circuit. Before I go to the dealers service dept any help PLEASE. ???

 

P0721/P0174 System too Lean


DTC P0621
Circuit Description
The powertrain control module (PCM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the PCM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. When the PCM turns ON the high side driver, the voltage regulator turns ON the field circuit. When the PCM turns OFF the high side driver, the voltage regulator turns OFF the field circuit.
The PCM monitors the state of the generator turn on signal circuit. The PCM should detect a low generator turn on signal circuit voltage when the key is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the PCM should detect a high generator turn on signal circuit. The PCM performs key ON and RUN tests to determine the status of the generator turn on signal circuit. During the key ON test, if the PCM detects a high generator turn on signal circuit voltage, DTC P0621 will set. DTC P0621 will also set, if during the RUN test, the PCM detects a low generator turn on signal circuit. When the DTC sets, the PCM will send a class 2 serial data message to the instrument panel cluster (IPC) to illuminate the charge indicator.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0621 Generator L-Terminal Circuit
Conditions for Running the DTC
The ignition is ON.
The engine speed is more than 1,000 RPM.
Conditions for Setting the DTC
The PCM detects the GEN L-Terminal active with the ignition ON.
The PCM detects the GEN L-Terminal inactive with the engine operating.
The above conditions are present for 6 seconds.
Action Taken When the DTC Sets

 

For the system lean codes, check your MAF and ensure no loose connector. If you have modified the air intake recently, check installation and orientation of MAF as well - it can be put in up side down!

Not sure what possible issue exists with the PCM curcuit code.

 

So the o2 sensors are not the problem? It looks like something only the dealer can fix. Any thing I can try other than checking the connectors?

 

Your O2 sensors were just sitting there on the exhaust?

 

Don't take your Vette to any auto parts store to get codes read... OR to Walmart..,
Go to a good sped shop and get it done right.

 

A word of caution -- some over the counter O2 sensors that claim to fit corvettes will not work properly ... be sure to take out your O2 and match it up properly ( if you replace it ) .. and you are correct .. there are four -- 2 upstream and 2 downstream.

 

Codes are codes... While the description may not be exact, any normal engine codes will have no issues being pulled. I could see issues with the TC/AH codes or airbag codes and such being pulled though... Once you have the codes, hop online to see what they are. No reason to spend extra money at a speed shop just to have codes pulled...

 

Save your nickles and dimes and get a $14 code reader:

Info from shop manual:

DTC Descriptors
DTC P0171: Fuel Trim System Lean Bank 1

DTC P0172: Fuel Trim System Rich Bank 1

DTC P0174: Fuel Trim System Lean Bank 2

DTC P0175: Fuel Trim System Rich Bank 2


Circuit/System Description
The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open Loop and Closed Loop (CL). During Open Loop, the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) input. During CL, the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0 percent. If the HO2S indicates a rich condition, the FT values will be below 0 percent. The short term FT values change rapidly in response to the HO2S voltage signals. The long term FT makes coarse adjustments in order to maintain an optimum air/fuel ratio. A block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term FT diagnostic is based on an average of cells currently being used. The ECM selects the cells based on the engine speed and load. The FT diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the evaporative emission (EVAP) canister is causing a rich condition.

If the ECM detects an excessively lean condition, DTC P0171 or P0174 sets. If the ECM detects an excessively rich condition, DTC P0172 or P0175 sets.

Conditions for Running the DTC
• DTCs P0030, P0036, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0117, P0118, P0120, P0121, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0201-P0208, P0220, P0300, P0301-P0304, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P1106, P1107, P1114, P1115, P1133, P1516, P2101, P2119, P2120, P2125, P2135, P2138, P2176 are not set.

• The engine is in Closed Loop status.

• The engine coolant temperature (ECT) is between -40 and +150°C (-40 and +302°F).

• The intake air temperature (IAT) is between -20 and +150°C (-4 and +302°F).

• The manifold absolute pressure (MAP) is between 10-255 kPa (1.45-37 psi).

• The vehicle speed is less than 134 km/h (83 mph).

• The engine speed is between 375-7,000 RPM.

• The mass air flow (MAF) is between 1-510 g/s.

• The barometric pressure (BARO) is more than 70 kPa (10.2 psi).

• The fuel level is more than 10 percent.

• This diagnostic runs continuously when the above conditions have been met.

Conditions for Setting the DTC
• The average long term FT weighted average value is more or less than a calibrated value.

• The above condition is present for approximately 3 minutes after the conditions for running the DTC have been met.

Action Taken When the DTC Sets
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second ignition cycle the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. The control module illuminates the malfunction indicator lamp (MIL) when one of the following occur:

• The control module detects the same fuel trim failure during 2 consecutive trips.

• The control module detects any fuel trim failure during any subsequent trip if the conditions at the time of failure meet the following criteria:

- The engine load is within 20 percent of the previous test that failed.

- The engine speed is within 375 RPM of the previous test that failed.

- The engine coolant temperature is in the same range of the previous test that failed.

Conditions for Clearing the MIL/DTC
• The control module turns OFF the malfunction indicator lamp (MIL) at the beginning of the fourth ignition cycle, after 3 ignition cycles that the diagnostic runs and does not fail.

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• A history DTC and related Freeze Frame data clears after 40 warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• Clear the MIL and the DTC with a scan tool.

Circuit/System Testing
P0171 or P0174
Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term FT parameter with a scan tool. The value should be less than approximately 20 percent with the engine running at operating temperature.

⇒ If the value is not less than 20 percent, inspect for the following:

• With the ignition ON and the engine OFF, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure .

⇒ Refer to DTC P0106 if the MAP sensor does not indicate the correct barometric pressure.

• With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be within 2-6 g/s at idle.

⇒ Refer to DTC P0101 or P1101 or DTC P0102 or P0103 if the MAF sensor parameter is not within 2-6 g/s at idle.

• Vacuum hoses for splits, kinks, and improper connections

• Insufficient fuel in the tank

• Low fuel pressure

• Fuel contamination

• Malfunctioning fuel injectors

• Missing, loose, or leaking exhaust components from the HO2S forward

• Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings

• The air induction system and the air intake ducts for leaks or for a missing air filter element

• A cracked EVAP canister

• Evaporative pipes obstructed or leaking

• The crankcase ventilation system for leaks

• The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system

• The HO2S signal circuit open, shorted to ground, or shorted to the low reference circuit

• Malfunctioning engine components