GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P012B: Supercharger Inlet Pressure Sensor Performance

Diagnostic Fault Information

SC Inlet Pressure Sensor

Circuit

Short to Ground

High Resistance

Open

Short to Voltage

Signal Performance

5-Volt Reference

P0107, P012C, P0452, P0641

P006D

P012C

P0641, P2229

P006D, P012B

SC Inlet Pressure Sensor Signal

P012B, P012C

P006D

P012C

P012D*

P006D, P012B

Low Reference

--

P006D, P012B

P012B, P012D

*

P006D, P012B

*Internal ECM or sensor damage may occur if the circuit is shorted to B+.

Typical Scan Tool Data

SC Inlet Pressure Sensor

Circuit

Short to Ground

Open

Short to Voltage

Operating Conditions: Ignition ON, engine OFF

Parameter Normal Range: BARO

5-Volt Reference

8-12 kPa

8-12 kPa

96-104 kPa

SC Inlet Pressure Sensor Signal

8-12 kPa

8-12 kPa

96-104 kPa

Low Reference

--

96-104 kPa

--

Circuit Description

Note: The following applies to the intake airflow system performance diagnostic that is used in this supercharged engine:

   • When referring to the supercharger intake manifold models, the plenum volume between the throttle body and the supercharger is considered to be the intake manifold.
   • When referring to engine pumping, the supercharger and the intercooler plenum are considered to be part of the engine.
   • The manifold absolute pressure (MAP) estimates are used in the engine air flow estimates. Air flow into the intake system must be the same as the air flow out of the intake system, the Intake Airflow Rationality Diagnostics (IFRD) calculates air flowing out of the engine based on MAP estimates, volumetric efficiency, and RPM.

The intake airflow system performance diagnostic provides the within-range rationality check for the mass air flow (MAF), supercharger inlet absolute pressure (SCIAP), MAP, by-pass valve stuck, and the throttle position (TP) sensors. This is an explicit model-based diagnostic containing 4 separate models for the intake system.

    • The throttle model describes the flow through the throttle body and is used to estimate the MAF through the throttle body as a function of barometric pressure (BARO), throttle position, intake air temperature (IAT), and estimated SCIAP. The information from this model is displayed on the scan tool as the MAF Performance Test parameter.
    • The first supercharger intake manifold model describes the pressure at the supercharger intake manifold and is used to estimate SCIAP as a function of the MAF into the intake manifold from the throttle body and the MAF out of the intake manifold caused by engine pumping. The flow into the supercharger intake manifold from the throttle uses the MAF estimate calculated from the above throttle model. The information from this model is displayed on the scan tool as the MAP Performance Test 1 parameter.
    • The second supercharger intake manifold model is identical to the first supercharger intake manifold model except that the MAF sensor measurement is used instead of the throttle model estimate for the throttle air input. The information from this model is displayed on the scan tool as the MAP Performance Test 2 parameter.
    • A fourth model is created from the combination and additional calculations of the throttle model and the first supercharger intake manifold model. The information from this model is displayed on the scan tool as the TP Performance Test parameter.
    • In addition 5 new models have been added, these models run in the background.

The estimates of MAF, SCIAP, and TP that are obtained from this system of models and calculations are then compared to the actual measured values from the MAF, SCIAP, and the TP sensors and to each other to determine the appropriate DTC to fail. The following table illustrates the possible failure combinations and the resulting DTC or DTCs.

Scan Tool Diagnostic Test Results

MAF Performance Test

MAP Performance Test 1

MAP Performance Test 2

TP Performance Test

DTCs Passed

DTCs Failed

--

--

OK

OK

P0101, P0121, P012B, P1101

None

OK

OK

Fault

OK

P0101, P0121, P012B, P1101

None

Fault

OK

Fault

OK

P0121, P012B, P1101

P0101

OK

Fault

Fault

OK

P0101, P0121, P1101

P012B

Fault

Fault

Fault

OK

P0121, P1101

P0101, P012B

--

--

OK

Fault

P0101, P012B, P1101

P0121

OK

OK

Fault

Fault

P0101, P0121, P012B, P1101

None

Fault

OK

Fault

Fault

P0101, P0121, P012B

P0101, P1101

--

Fault

Fault

Fault

P0101, P0121, P012B

P0101, P1101

Conditions for Running the DTC

    • DTCs P0096, P0097, P0098, P0102, P0103, P0111, P0112, P0113, P0117, P0118, P0120, P0121, P0128, P012C, P012D, P0220, P0401, P0405, P0506, P0507, P1404, P2135 are not set.
    • The engine is running.
    • The engine coolant temperature (ECT) is between 70-129°C (158-264°F).
    • The IAT is between -7 to +125°C (+19 to +257°F).
    • The change in the TP is less than 5 percent.
    • The above enabling criteria must be stable for more than 5 seconds.
    • This DTC runs continuously when the above conditions are met.

Conditions for Setting the DTC

The engine control module (ECM) detects that the actual measured airflow from the MAF, MAP, SC Inlet Pressure and TP sensors is not within a range of the calculated airflow that is derived from the system of models by greater than a calibrated threshold, for greater than 10 seconds.

Action Taken When the DTC Sets

DTC P012B is a Type B DTC.

Conditions for Clearing the MIL/DTC

DTC P012B is a Type B DTC.

Diagnostic Aids

This DTC may set due to any of the following conditions:

    • Any condition that can cause the MAF, MAP, SCIAP, and TP sensors to be shifted in value
    • A resistance of 10-20 ohms on the 5-volt reference or low reference circuits of the SCIAP sensor
    • Any condition that may cause the supercharger by-pass valve to bind or stick in either the open or closed positions

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Description and Operation Reference

    •  Boost Control System Diagnosis
    •  Supercharger Description and Operation
    •  Boost Control System Description

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

    • J 35555 Metal Mityvac
    • J 23738-A Mityvac

Circuit/System Verification

  1. Verify DTCs P0102, P0103, P0106, P0107, P0108, P0121, P0641, P0651, P2228, or P2229 are not set.
  2. If the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
  3. Ignition ON, observe the MAP and SC Inlet Pressure Sensor kPa parameters with a scan tool. Start the engine and let it idle. The MAP Sensor and SC Inlet Pressure Sensor kPa parameters should decrease and closely match each other.
  4. If the MAP Sensor parameter does not decrease and closely match the SC Inlet parameter, refer to DTC P0106.
  5. Ignition ON, depress the accelerator pedal completely to wide open throttle (WOT) and observe the TP Indicated Angle parameter with a scan tool. The TP Indicated Angle parameter should read 98-100 percent.
  6. If the TP Indicated Angle parameter is not within the specified range, refer to DTC P1516, P2101, P2119, or P2176.
  7. Ignition ON, perform a snapshot of the throttle actuator control (TAC) data while performing the following actions. Refer to Scan Tool Snapshot Procedure.
  8. 4.1. Slowly depress the accelerator pedal to WOT and then slowly release the pedal. Exit from the snapshot and review the data.
    4.2. Compare the TP Sensor 1 and the TP Sensor 2 parameters, frame by frame. The difference between the parameters should be less than 4 percent.
    If the difference is greater than 4 percent, refer to DTC P0120, P0122, P0123, P0220, P0222, P0223, or P2135.
  9. Road test the vehicle and perform a brief wide open throttle (WOT) acceleration from 30 mph. The MAP sensor parameter on the scan tool should increase rapidly. This increase should be from approximately 35 kPa at idle to greater than 135 kPa.
  10. If less than the specified range, refer to Boost Control System Diagnosis.
  11. A skewed or stuck ECT, BARO, MAP, MAF/IAT, or IAT sensor 2 will cause the calculated models to be inaccurate and may cause this DTC to run when it should not. Refer to Temperature Versus Resistance and Altitude Versus Barometric Pressure.
  12. Operate the vehicle within the Conditions for Running the DTC to verify that the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Note: 

   • You must perform Circuit/System Verification before proceeding with the Circuit/System Testing.
   • The harness connectors for the following sensors are of the same configuration but are not interchangeable. Review the engine controls schematics for the BARO sensor and for the SCIAP sensor and note the circuit colors. Inspect the wiring harness of the BARO sensor for the proper connections. Inspect the wiring harness of the SCIAP sensor for the proper connections.

  1. Visually and physically inspect the integrity of the entire supercharger air induction system, for any of the following conditions:
  2. • A restricted or collapsed air intake duct
    • A misaligned or damaged air intake duct
    • A dirty or deteriorating air filter element
    • Any objects blocking the air inlet probe of the MAF/IAT sensor
    • Any contamination or debris on the sensing elements in the probe of the MAF/IAT sensor
    • Any water intrusion in the induction system
    • Any vacuum leak downstream of the MAF/IAT sensor
    • An intake manifold leak
         ⇒If a condition is found, repair as necessary.
  3. Visually and physically inspect all vacuum lines for cracking, loose fit, restrictions and proper routing at the following locations:
  4. • The SCIAP sensor
    • The MAP sensor
    • The by-pass valve solenoid
    • The by-pass valve actuator
         ⇒If a condition is found, repair as necessary.
  5. Visually and physically inspect the by-pass valve and cable for any of the following conditions:
  6. • A binding or sticking in the open or closed position
    • A binding when opening or closing
    • An incorrectly adjusted cable
    • Any damage
         ⇒If any of the above conditions are found, refer to Supercharger Cleaning and Inspection.
  7. Ignition OFF, disconnect the harness connector at the SCIAP sensor.
  8. Ignition OFF for 90 seconds, test for less than 5 ohms between the low reference circuit terminal A and ground.
  9. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  10. Verify the scan tool SC Inlet Pressure Sensor parameter is less than 20 kPa.
  11. If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  12. Install a 3A fused jumper wire between the 5-volt reference circuit terminal C and the signal circuit terminal B. Verify the scan tool parameter is greater than 95 kPa.
  13. If less than the specified range, test the signal circuit for a short to ground, open/high resistance. If the circuit tests normal, replace the ECM.
  14. If all circuits test normal, test or replace the SCIAP sensor.

Component Testing

Note: You must perform the Circuit/System Testing before proceeding with the Component Testing.

  1. Ignition OFF, remove the SCIAP sensor.
  2. Install a 3A fused jumper wire between the 5-volt reference terminal C of the sensor and a 5-volt reference.
  3. Install a jumper wire between the low reference terminal A of the sensor and ground.
  4. Install a jumper wire at the signal terminal B of the SCIAP sensor.
  5. Connect a DMM between the jumper wire from terminal B of the SCIAP sensor and ground.
  6. Ignition ON, with the J 23738-A Mityvac or J 35555 Metal Mityvac slowly apply vacuum to the sensor while monitoring the voltage on the DMM. The voltage should vary between 4.9-0.4 volts, without any spikes or dropouts.
If the voltage is not within the specified range or is erratic, replace the SCIAP sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Supercharger Air Inlet Pressure Sensor Replacement
    •  Control Module References for ECM replacement, setup, and programming