Circuit Description
The Catera multi-ram system uses variable air induction tuning in order to achieve maximum performance and efficiency over the entire operating range of the engine. The system consists of two main parts. The intake manifold contains the intake plenum switchover valve. This vacuum operated valve is essentially a moveable divider that changes the airflow characteristics of the intake manifold. The vacuum to the valve is controlled by an engine control module (ECM) controlled solenoid valve. The second part is the intake resonance switchover valve. This vacuum operated valve is located in the air intake duct assembly in front of the engine. This is also basically a moveable divider that changes the tuning of the air intake system. The vacuum to the valve is controlled by an ECM controlled solenoid valve. By opening and closing these valves independently, in different combinations, four different air flow configurations can be created, each optimized to a particular set of engine operating conditions.
Both of the solenoid valves are supplied power via the engine controls power relay, switched B+). Both of the solenoid valves have a control circuit to the ECM. The ECM controls a valve by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near the battery voltage. If the fault detection circuit senses a voltage other than what is expected, a diagnostic trouble code (DTC) will set.
The ECM will monitor the circuit for the following:
| • | A short to ground |
| • | A short to voltage |
| • | A open circuit |
| • | An internally shorted or excessively low resistance circuit |
When the ECM detects any of the above malfunctions, this DTC will set and the affected driver will be disabled. The ECM will continue to test the circuit and if the fault goes away, the driver will be reactivated.
Conditions for Running the DTC
| • | The ignition voltage is between 9.0 and 17.0 volts. |
| • | The engine speed is greater than 80 RPM. |
Conditions for Setting the DTC
A short to ground, an open circuit, or a short to battery voltage is detected on the control circuit.
Action Taken When the DTC Sets
The ECM will not illuminate the malfunction indicator lamp (MIL).
Conditions for Clearing the MIL/DTC
| • | The DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other non-emission related diagnostic. |
| • | The scan tool clears the MIL/DTC. |
Diagnostic Aids
Use the Connector Test Adapter Kit J 35616 for any test that requires probing the ECM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.
Check for the following conditions:
| • | Poor connections at the ECM or at the component. Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Engine Control Module Diagnosis for the proper procedure. |
| • | Switched harness. Inspect the IAT sensor electrical connector and the Intake Resonance Switchover Valve electrical connector for being switched. This can cause the IAT sensor reading to remain constant. Allow the vehicle to idle a few minutes and, using the scan tool, observe the IAT sensor. |
| • | Misrouted harness. Inspect the harness in order to ensure that the harness is not routed too close to any high voltage wires such as spark plug leads, or too close to any high current devices such as the alternator, the motors, the solenoids, etc. |
| • | Damaged harness. Inspect the wiring harness for any damage. If the harness appears to be OK, observe the scan tool while moving the related connectors and the wiring harnesses. A change in the display may help in order to locate the fault. |
Refer to Symptoms for the Intermittents.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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Listen for an audible click when the valve operates. Repeat the commands as necessary.
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This check can detect a partially shorted coil which would cause excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When warm the coil may open (amps drop to 0), or short (goes above 0.75 amp).
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If no trouble is found in the control circuit or the connection at the ECM, the ECM may be damaged, however, this is an extremely unlikely failure.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System check? | -- | ||
Does the valve turn on and off with each command? | -- | |||
Does the current draw a measure within the range shown? | 0.1 to 0.75 A | Refer to Diagnostic Aids | ||
4 |
The DVM should display an infinite resistance. Does the DVM display an infinite resistance? | -- | ||
5 |
Does the test light turn on and off with each command? | -- | ||
6 | Probe the Switched B+ circuit in the valve harness connector with the test light connected to ground. The test light should illuminate. Does the test light illuminate? | -- | ||
7 |
Does the valve operate? | -- | ||
8 | Check the connections and the related wiring at the solenoid and the ECM. Was a problem found and corrected? | -- | ||
9 | Repair the valve control circuit. Is the action complete? | -- | -- | |
10 | Repair the Switched B+ circuit to the valve. Is the action complete? | -- | -- | |
11 | Replace the valve. Is the action complete? | -- | -- | |
12 | Check for a poor connection or poor terminal tension at the ECM harness connector. Refer to Electrical Diagnosis in Engine Electrical, and Troubleshooting Procedures for the proper procedure. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis . Was a problem found and corrected? | -- | ||
|
Important: This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle. Replace the ECM. Refer to Engine Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
14 |
Is this DTC set? | -- | ||
15 | Were there any additional DTCs noted during the Powertrain OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | The System is OK |
