Notice: Do not open the DERM case for any reason. Touching the connector pins, or the soldered components may cause electrostatic discharge damage. Replacement is the only way to repair a malfunctioning DERM.

Supplemental Restraint Diagnostic Energy Reserve Module (DERM)

The DERM performs the following functions in the Supplemental Restraint System (SRS):

The DERM is connected to the SRS wiring harness by a 24-way connector. When the DERM harness connector is disconnected, a shorting bar connects the AIR BAG warning lamp to ground . This causes the AIR BAG warning lamp to light up whenever the ignition switch is at the RUN or the START position.

AIR BAG Warning Lamp

The AIR BAG warning lamp notifies the driver of Supplemental Restraint System (SRS) malfunctions. Ignition voltage is applied to the AIR BAG warning lamp when the ignition switch is at the RUN or START positions. The supplemental restraint Diagnostic Energy Reserve Module (DERM) controls the lamp by providing ground with a lamp driver. The AIR BAG warning lamp does the following tasks:

For proper AIR BAG warning lamp operation, refer to Instrument Panel and Gages in Section 8C.

Supplemental Restraint Arming Sensor

The supplemental restraint arming sensor is a protective switch. It is located in the high side (power side) of the deployment loop. The supplemental restraint arming sensor closes at low level velocity changes (lower than the supplemental restraint discriminating sensors). This ensures that the supplemental restraint steering wheel inflator module connects directly to the 36 VLR output of the supplemental restraint Diagnostic Energy Reserve Module (DERM) or Ignition 1 voltage when either of the discriminating sensors closes.

The supplemental restraint arming sensor consists of the following components:

The sensing element closes the switch contacts when the velocity of the vehicle changes quickly enough to indicate a potential need for deployment.

The 5.1 kohms diagnostic resistor is connected in parallel with the switch contacts. This allows a small amount of current to flow through the deployment loop during normal operation. The current flow results in current drops across each component that is within the deployment loop. The DERM monitors these voltage drops in order to detect circuit or component malfunctions. The 2.49 kohms diagnostic resistor is connected in parallel with the diodes. This allows the DERM to monitor the voltage that is applied to the high side of the deployment loop. The two diodes that are in the supplemental restraint arming sensor isolate the 36 VLR output of the DERM from the Ignition 1 voltage.

Supplemental Restraint Discriminating Sensors

There are two supplemental restraint discriminating sensors in the Supplemental Restraint System (SRS). These are the LH forward supplemental restraint discriminating sensor and the RH forward supplemental restraint discriminating sensor. They are wired in parallel on the low side (ground side) of the deployment loop. These sensors close when the velocity of the vehicle changes severely enough to indicate a potential need for deployment.

The supplemental restraint discriminating sensors consist of the following components:

The sensing element closes the switch contacts when the velocity of the vehicle changes severely enough to warrant deployment. A diagnostic resistor is connected in parallel with the switch contacts. These contacts are located within each of the supplemental restraint discriminating sensors. The parallel resistors supply a ground path for a current. This current passes through the deployment loop during normal operation. The current flow results in drops in voltage across each component within the deployment loop. The supplemental restraint Diagnostic Energy Reserve Module (DERM) monitors these voltage drops in order to detect circuit or component malfunctions.

Supplemental Restraint Steering Wheel Module Coil

The supplemental restraint steering wheel module coil consists of two coils which carry currents. These coils are attached to the steering column. The coils allow rotation of the steering wheel. They also maintain continuous contact between the deployment loop and the supplemental restraint steering wheel inflator module.

A shorting bar is located on the yellow 2-way connector at the base of the steering column. The shorting bar connects the supplemental restraint steering wheel module coil to the SRS wiring harness. The shoring bar shorts the circuits to the supplemental restraint steering wheel module coil and the inflator module when the 2-way connector is disconnected. This helps prevent unwanted deployment of the air bag while servicing the steering column or other SRS components.

Supplemental Restraint Steering Wheel Inflator Module

The inflator module is located on the steering wheel hub. The inflator module consists of an inflatable bag and an inflator. An inflator is a canister of gas generating material and an initiating device. During a crash that is of sufficient force to close both the supplemental restraint arming sensor and at least one of the supplemental restraint discriminating sensors at the same time, a current flows through the loop. A current passing through the initiator ignites the material that is in the inflator module. The gas produced from this reaction rapidly inflates the air bag.

There is a shorting bar on the inflator module side of the upper steering column connector. The shorting bar connects the supplemental restraint steering wheel module coil to the inflator module. The shorting bar shorts the inflator module circuit then the upper steering column connector becomes disconnected. This shorts the inflator in order to help prevent unwanted deployment of the air bag when servicing the inflator module or the steering column.

Steering Column

The steering column is energy absorbing. It is designed to compress in a frontal crash in order to decrease the chance of injury to the driver.

Knee Bolster

The knee bolster absorbs energy and controls the driver's forward movement during a frontal crash.

Definitions

Supplemental Restraint System (SRS) component/system definitions

The air bag is an inflatable cloth cushion that is designed to deploy in certain frontal crashes. It supplements the seatbelt protection by distributing the impact load more evenly over the vehicle occupant's head and torso.

B+ is a battery voltage. This represents the battery voltage at the time of the indicated measurement. With the ignition switch ON and the engine not running, the system voltage will likely be between 11.5 and 12.5 volts. At engine idle, the voltage may be 14 to 16 volts. The voltage could be as low as 10 volts during engine cranking.

Under normal operation this occurs when the ignition switch transitions from the OFF position to the RUN position. The supplemental restraint Diagnostic Energy Reserve Module (DERM) causes the AIR BAG warning lamp to flash seven times if no malfunctions are detected. The bulb test will also occur if IGNITION 1 voltage exceeds 17.1 volts and returns to the normal operating voltage range. The presents of a malfunction could prevent the DERM from flashing the warning lamp.

Circuit.

Test preformed by the supplemental restraint Diagnostic Energy Reserve Module (DERM) on the Supplemental Restraint System (SRS) during each 100 millisecond interval. The IGNITION 1 voltage at the DERM must be within the normal operating voltage range for continuous monitoring to occur. These tests follow the POWER-ON tests.

A base line parallel to the plane of the underbody or frame of the vehicle. All vertical measurements originate from this base line.

To inflate the air bag.

The circuit that supply current to the inflatable restraint steering wheel inflator module to deploy the air bag.

A DTC is a 5 digit alpha numerical designator that is used by the supplemental restraint Diagnostic Energy Reserve Module (DERM) in order to indicate specific Supplemental Restraint System malfunctions. And DTC can be displayed and cleared on a scan tool.

An output of the supplemental restraint Diagnostic Energy Reserve Module (DERM) that supplies a low resistance path to ground for the supplemental restraint steering wheel inflator module circuit during the Initiator Assembly Resistance Test.

Digital Volt Multimeter or Digital Volt Ohm Multimeter; J 39200.

Each diagnostic trouble code is assigned a priority. This priority is based on the detectability with other DTCs present. The priority only corresponds to the detectability of the malfunction. The priority does not relate to the critically of the malfunction with respect to deployment or non-deployment under any particular condition.

A battery voltage (B+) circuit which is only powered with the ignition switch in the RUN or START positions.

With the ignition switch ON, the voltage at the supplemental restraint Diagnostic Energy Reserve Module (DERM) Ignition 1 inputs is within the normal operating voltage range for at least ten seconds before turning the ignition switch OFF.

An electrical component that is inside the supplemental restraint steering wheel inflator module. When sufficient current flows, the supplemental restraint steering wheel inflator module sets off the chemical reaction which inflates the air bag.

This test checks for the following items:

1. The correct supplemental restraint Diagnostic Energy Reserve Module (DERM) configuration for the vehicle
2. Shorts for Ignition 1 in the deployment loop
3. High resistance or opens in the Driver Side High and the Driver Side Low circuits
4. Measures the resistance of the inflator assembly.

The inflator assembly consists of the following items:

•	The initiator

•	The supplemental restraint steering wheel module coil

•	Connectors

•	Associated wiring

Each test is performed once per ignition cycle in which no malfunctions are detected during Turn-ON or Continuous Monitoring.

A sensor on the low side (ground side) of the deployment loop. The sensor is calibrated to supply ground to the supplemental restraint steering wheel inflator module when the vehicle velocity changes are severe enough to warrant the deployment of the air bag.

The voltage that is measured between the supplemental restraint Diagnostic Energy Reserve Module (DERM) Ignition 1 terminal and the ground terminals. The voltage should be between 7.25 and 16 volts.

A sensor on the low side (ground side) of the deployment loop. The sensor is calibrated to supply ground to the supplemental restraint steering wheel inflator module when the vehicle velocity changes are severe enough to warrant the deployment of the air bag.

The scan tool is an off-board computer that is used in order to read diagnostic information from an on-board computer. This is done via the data link connector.

Serial data is information that represents the status of the Supplemental Restraint System (SRS).

The SRS is the Supplemental Restraint System.

The Supplemental Restraint System (SRS) Wiring Harness is made up of the wires and the connectors which electrically connect the components in the SRS.

The supplemental restraint arming sensor is on the high side (power side) of the deployment loop. The supplemental restraint arming sensor is calibrated to supply voltage to the supplemental restraint steering wheel inflator module when the velocity of the vehicle changes quickly enough to warrant arming the air bag. This is done in preparation for deployment.

A 4-way connector that is located on the top of the LH side wheelhouse. It connects the front of the dash wiring harness to the supplemental restraint arming sensor jumper harness.

The module which provides reserve energy to the deployment loop. The DERM also performs diagnostic monitoring on all of the Supplemental Restraint System (SRS) components.

A 4-way connector which is located on the top of the LH side wheelhouse. It connects the front of the dash wiring harness to the forward sensor harness.

The supplemental restraint steering wheel inflator module is located in the steering wheel hub. The supplemental restraint steering wheel inflator module consists of the following components:

The supplemental restraint steering wheel module coil consists of two coils which carry currents. These coils are attached to the steering column. The coils allow rotation of the steering wheel. They also maintain continuous contact between the deployment loop and the supplemental restraint steering wheel inflator module.

The voltage that is available at the battery at the time of the indicated measurement. with the ignition switch ON and the engine not running, the system voltage will likely be between 11.5 and 12.5 volts. At idle, the voltage may be 14 to 16 volts. During engine cranking, the voltage could be as low as 10 volts.

The supplemental restraint Diagnostic Energy Reserve Module (DERM) performs this test on the SIR system once during each ignition cycle. This is done immediately after Ignition 1 voltage is applied to the DERM and before Continuous Monitoring.

The portions of the Initiator Assembly Resistance Rest that are repeated every ten minutes during an ignition cycle. This is the test that checks for shorts to Ignition 1 in the deployment loop.

This is the energy supply from the supplemental restraint Diagnostic Energy Reserve Module (DERM) which provides deployment power when the vehicle voltage is low or lost in a frontal crash.

Charging of the 36 VLR power supply is inhibited briefly during Turn-ON. This allows the detection of certain malfunctions related to Ignition 1 voltage. These malfunctions cannot be tested with 36 volts present.