For 1990-2009 cars

### Circuit Description

When the ignition switch is first turned ON, the SDM will perform tests to diagnose critical malfunctions within itself. Upon passing these tests "Ignition 1", VLR, and deployment loop voltages are measured to ensure they are within their respective normal voltage ranges. The SDM monitors the voltage at "Driver Side LO" terminal A2 and "Passenger Side LO" terminal A4 to detect shorts in ground in the passenger inflator module circuits.

### DTC Will Set When

The VLR power supply in the SDM is in its normal operating range and at least one of the two inflator modules is not open. Then, if the voltage measured at "Driver Side LO" is greater than 3 volts and the voltage measured at "Passenger Side LO" is less than or equal to three volts for 500 milliseconds during "Continuous Monitoring" or "Current Source Diagnostic," DTC1018 will set.

### Action Taken

SDM turns ON the AIR BAG telltale lamp and sets DTC B1018 and also B1071. DTC B1018 will take precedence over DTCs B1015,B1016,B1018,B1021 and B1022.

### DTC Will Clear When

The fault condition is removed and the SDM is replaced. DTC B1018 will remain current, regardless if the ignition switch is turned OFF or a Scan Tool "Clear Codes" command is issued until the faulty wiring or component is repaired or replaced and the SDM is replaced.

### Diagnostic Aids

It is critical to diagnose all circuitry before replacing the SDM. If the malfunction still exists, the new SDM will be damaged. An intermittent condition is likely to be caused by a short to ground in the passenger inflator module circuits. Inspect circuits 1403 and 1404 carefully for cutting and chaffing. If the wiring pigtail of the passenger inflator module is damaged, the module must be replaced. If no circuit or component failures are located, after a complete and thorough inspection, the fault may have occurred internally to the SDM.

The test for this diagnostic trouble code is run during "Continuous Monitoring" and "Current Source Diagnostics," unless DTC B1017 or B1026 is detected.

When measurements are requested in this chart use SA 91114NE DVM with correct terminal adapter from SA 9206Z. When a check for proper connection is requested refer to Intermittent and Poor Connections in this manual. When a wire connector or terminal repair is requested, use the proper repair parts and refer to Wiring Repairs .

Caution: Be careful when you handle a sensing and diagnostic module (SDM). Do not strike or jolt the SDM. Before applying power to the SDM:

• | Remove any dirt, grease, etc. From the mounting surface.

• | Position the SDM horizontally on the mounting surface.

• | Tighten all of the SDM fasteners and SDM bracket fasteners to the specified torque value.

Failure to follow the correct procedures could cause air bag deployment, personal injury, or unnecessary SIR system repairs.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This test determines whether the malfunction is occurring in the passenger inflator module, or the circuitry.

2. This test checks for a short from "Passenger Side LO" to ground.

3. This test checks for a short from "Passenger Side HI" to ground, or a SDM integrity problem.

Step | Action | Yes | No
--- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - SIR? | Go to Step 2 | Go to SIR Diagnostic System Check
2 |

1. Turn OFF ignition.
2. Disconnect driver and passenger inflator modules, yellow two-way connectors located at the base of the steering column and under the I/P top cover. Leave driver inflator module connected.
3. Connect SIR driver/passenger load tool SA9409Z-A to passenger inflator module harness connector.
4. Turn ON ignition.
5. Read the Passenger Sense LO Voltage (PASS SENS VOLT) on Scan Tool.

Is Passenger Sense LO Voltage less than 3.3 volts?

Go to Step 3

Go to Step 5

3 |

1. Turn OFF ignition.
2. Disconnect SIR driver/passenger load tool.
3. Disconnect SDM.
4. If OK, then measure resistance from SDM harness connector terminal A4 to terminal A6 (ground).

Does DVM display OL (Infinite)?

Go to Step 4

Go to Step 5

4 | Measure resistance on the SDM harness connector from terminal lA1 to terminal A6 (ground). Does DVM display OL (Infinite)? | Go to Chart A | Go to Step 6
5 | Repair short from circuit 1404 to ground. Go to Step 7 | -- | --
6 | Repair short from circuit 1403 to ground. Go to Step 7. | -- | --
7 |

1. Inspect wiring pigtail to passenger inflator module for damage. Determine and repair the cause of damage.
2. Replace passenger inflator module. Refer to Passenger Inflator Module.
3. Go to Step 7

Go to Step 8

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8 |

1. Replace SDM. Refer to Sensing and Diagnostics Module (SDM).
2. Reconnect all SIR system components. Ensure all components are properly mounted.
3. Clear SIR diagnostic trouble codes.
4. Repeat SIR Diagnostic System Check.

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