Seat System: Overview Cadillac STS I

Test Description

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

1. 2: This test determines which directional motor exhibits excessive current.
2. 3: This test determines if the suspect motor has an internal short to ground.
3. 9: This test verifies the repair.

DTC B1335

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

1. 2: This step checks the existing state of the driver's seat switch by using the current state of the signal parameter. If all of the seat switch parameters display active, possibly one of the seat switch signal circuits is shorted to voltage.
2. 4: When the seat adjuster switch is disconnected, this step determines if the seat switch contacts are stuck closed, or if one of the switch signal circuits is possibly shorted to battery positive voltage.

DTC B1735, B1740, B1745, B1750, B1755, B1760, B1815, B1820, B1830, B1835, B1840, B1845, B1940, or B1945

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

1. 3: This step tests for the proper operation of the circuit in the high voltage range.
2. 4: This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

DTC B1825, B1850, B1860, B2355, B2365, or B2375

Symptoms - Seats

1. Perform the «Diagnostic System Check - Vehicle»(ref-197532-S30271296932005101200000) in Vehicle DTC Information, before using the symptom tables in order to verify that all of the following are true: There are no DTCs set. The control module(s) can communicate via the serial data link.
2. Refer to the system description and operation from the following list in order to familiarize yourself with the system functions: «Power Seats System Description and Operation (w/o A45)»(ref-197561-S06063471102005101200000) «Power Seats System Description and Operation (with A45 Disabled)»(ref-197561-S12392654532005101200000) «Lumbar Support Description and Operation (with A45 enabled)»(ref-197561-S10776050562005101200000) «Lumbar Support Description and Operation (w/o A45)»(ref-197561-S13444944762005101200000) «Lumbar Support Description and Operation (with A45 disabled)»(ref-197561-S18707889822005101200000) «Heated/Vented Seat Description and Operation»(ref-197561-S12155348712005101200000) «Heated Seats Description and Operation (Rear)»(ref-197561-S28805445692005101200000) «Memory Seats Description and Operation»(ref-197561-S11496795382005101200000)

The number below refers to the step number on the diagnostic table.

1. 8: This step tests the integrity of the signal circuits of the seat adjuster switch. If the fuse in the jumper wire opens when you perform this test, a short to ground may have occurred.

Power Seat Inoperative (with A45)

The number below refers to the step number on the diagnostic table.

1. 3: This step determines if the vented seat system is totally inoperative.
2. 4: This step determines which part of the seat is inoperative, the seat cushion or seat back.
3. 9: This step tests the integrity of the PWM serial data signal circuit from the memory seat module. This signal is a momentary 35 millisecond one shot pulse signal that is monitored through a momentary voltage change in the voltmeter when the switch is pressed. In order to accurately recognize the change in voltage, the voltmeter reading should be stable before performing this test.
4. 12: This step determines if the seat cushion blower has an internal short to ground or voltage.
5. 15: This step determines if the seat back blower has an internal short to ground or voltage.

Vented Seat Inoperative

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

1. 3: This step determines if the heated seat system is totally inoperative.
2. 4: This step determines if the seat is completely inoperative, or if just one of the 2 seat cushions is inoperative.
3. 5: This step determines which part of the seat is inoperative, the seat cushion or seat back.
4. 10: This step tests the integrity of the heated seat switch signal from the memory seat module. This signal is a momentary 35 millisecond one shot pulse signal that is monitored through a momentary voltage change in the voltmeter when the switch is pressed. In order to accurately recognize the change in voltage, the voltmeter reading should be stable before performing this test.

Heated Seat Inoperative

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

1. 3: This step determines if the rear heated seat system is totally inoperative.
2. 4: This step determines if the seat is completely inoperative, or if just one of the two seat cushions is inoperative.
3. 16: This step determines if the temperature sensor is open or if one of the sensor circuits is open. A short to battery voltage in the sensor signal circuit will open the sensor.

Heated Seat Inoperative - Rear

Power Seats System Description and Operation (w/o A45)

The passenger power seat system consists of the following components

1. Seat Adjuster Switch
2. Seat Horizontal Motor
3. Seat Front Vertical Motor
4. Seat Rear Vertical Motor
5. Seat Recline Motor
6. SEATS Circuit Breaker 30 A

Power Seats System Description and Operation (with A45 Disabled)

The driver power seat system with a non-memory configured memory seat module (MSM) consists of the following components

1. Memory Seat Module
2. Seat Adjuster Switch
3. Seat Horizontal Motor
4. Seat Front Vertical Motor
5. Seat Rear Vertical Motor
6. Seat Recline Motor
7. PWR Seat Circuit Breaker 30 A
8. MEM T&T Fuse 10 A

Heated/Vented Seat Description and Operation

The heated/vented seat system consists of the following components

1. Heated/Vented seat switch
2. Climate control seat module
3. HVAC control module
4. Memory seat module (MSM)
5. Seat cushion heater element
6. Seat back heater element
7. Temperature sensor
8. Seat cushion blower motor
9. Seat back blower motor
10. RF HTD ST/S-BAND Fuse 20 A
11. IGN 3 Fuse 10 A
12. DPM Fuse 10 A

Heated Seat Operation

When the ignition is turned to the ON position, the heated/vented seats will initialize in the OFF state. When the heated seat switch is pressed once, the climate control seat module applies battery positive voltage through the heated seat element supply voltage circuit to the seat cushion and seat back heating elements, initially setting the seat temperature to high heat. Then with each additional activation of the switch, the climate control seat module will cycle the temperature setting to MED, LOW, and OFF. The module will also turn off the heated seat function whenever the ignition switch is turned to the OFF position.

Vented Seat Modes of Operation

When the ventilation seat system is active, it is designed to draw cabin air around and away from the occupant through small holes in the seat cushion and seat back covers, through channels in the foam pad, and then through the blower motor exhausting the waste air under the seat cushion.

Battery positive voltage is supplied at all times to the driver seat blower motors from the DPM Fuse located in the left rear fuse block. Battery positive voltage is also supplied at all times to the front passenger seat blower motors from the RF HTD ST/S BAND Fuse located in the right rear fuse block. Both, the driver seat and passenger seat blower motors are grounded through their ground circuits and G307. When a vented seat switch is pressed, the climate control seat module sends a low side pulse width modulation (PWM) signal through the blower motor control circuits to the seat cushion and seat back blower motors indicating the vented seat command. In response to this signal, the logic in the blower motors set the blower speed to the switch set point. Both blower motors then run drawing cabin air around and away from occupant. The following describes the High, MED, and Low ventilation modes of operation

1. High Ventilation This mode cancels all previous modes and initiates a ventilation cycle with the Under-Cool and Super-Cool Features active. See below for the description of these features. In the high mode, both the seat cushion and seat back blowers are ON at a 95 percent duty cycle that provides 100 percent blower performance.
2. Medium Ventilation This mode operates identical to the High Ventilation setting with the exception that the blowers are ON at a 85 percent duty cycle that provides 80 percent blower performance.
3. Low Ventilation This mode also operates identical to the High Ventilation setting with the exception that the blowers are ON at a 75 percent duty cycle that provides 60 percent blower performance.

During vented seat modes of operation, the climate control seat module uses Under-cool and Super Under-cool Features in order to keep the seat temperature above pre-determined set point temperatures. The following describes these features

1. Under-Cool Feature The under-cool feature set point is 15°C (59°F). The climate control seat module under-cool feature is active when the system is in any one of the 3 High, MED, or Low ventilation modes. The under-cool feature will initiate a heat cycle when it detects that the seat temperature reached its set point of 15°C (59°F). This means that if the seat temperature reaches this set point, it is possible for both, the blowers and heaters to be on at the same time. Then if the control module does not detect that the operating temperature is above the set point within 90 seconds of the initiation of under-cool mode, the module will shut down and cease operation.
2. Super Under-Cool Feature The super under-cool feature set point is 10°C (50°F). The super under-cool feature is also active when the system is in any of the three ventilation modes. This feature is meant as a secondary precautionary measure. The super under-cool feature will deactivate the blower motors and initiate a heat cycle when it detects that the seat temperature reached its set point of 10°C (50°F). This means that it is possible for the seat heaters to be on and the blowers off while in the ventilation mode. If the control module does not detect that the operating temperature is above the set point within 90 seconds of the initiation of super under-cool mode, the module will shut down and cease operation.

Modes of Operation

There is 1 mode available for heated seat operation; both the seat cushion and seat back heat turn on and off together. When a heated seat temperature signal request is received, the heated seat module will activate both the seat cushion and seat back heating elements.

Heated Seat Switch/LED Indicators and Operation

The left and right rear heated seats are controlled by separate heated seat switches both located in the rear climate control panel (RCCP). Battery positive voltage is supplied to the RCCP by the rear heated seat module. The rear heated seat module controls the heated seat operation for both, the left and right rear heated seats, and the heated seat switch temperature indicators.

The following describes the sequence of operation and how the heated seat module responds to each of the switch inputs.

1. High Temperature: When the heated seat switch is pressed once, battery positive voltage is applied through the switch contacts and the switch signal circuit to the heated seat module indicating the high heat request. In response to this signal, the module applies battery positive through the heating element supply voltage circuits to the seat cushion and seat back heating elements. At the same time, it activates the low side drivers that supply a ground through the heating element control circuits to the seat heating elements. The module then applies a ground through the high temperature indicator control circuit illuminating the high temperature indicator to indicate the high temperature mode.
2. Medium Temperature: When the switch is pressed a second time, the heated seat module sets the temperature level to medium heat. Then it removes the ground from the high temperature indicator and applies ground to the medium temperature indicator to indicate the medium temperature mode.
3. Low Temperature: When the switch is pressed a third time, the heated seat module sets the temperature level to low heat. Then it removes the ground from the medium temperature indicator and applies ground to the low temperature indicator to indicate the low temperature mode.
4. System Off State: When the switch is pressed a fourth time, the heated seat module removes the battery voltage and grounds from the heating elements. Then it removes the ground from the low temperature indicator, indicating the system off state.

Memory Seats Description and Operation

The memory seat system consists of the following components

1. Memory seat module (MSM)
2. Seat adjuster switch
3. Seat lumbar switch
4. Seat horizontal motor
5. Seat front vertical motor
6. Seat rear vertical motor
7. Seat recline motor
8. Lumbar horizontal motor
9. Lumbar vertical motor
10. Seat horizontal position sensor
11. Seat front vertical position sensor
12. Seat rear vertical position sensor
13. Seat recline position sensor
14. Lumbar horizontal positional sensor
15. Lumbar vertical position sensor
16. Seats Circuit Breaker 30 A
17. DPM Fuse 10 A

The memory seat module (MSM) is referenced in the Tech 2 as the driver position module (DPM).