Code
B1820
HUMMER
B — Body
Driver Recline Rearward Switch Circuit Malfunction
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the recline switch circuit
- Poor or corroded connector or terminal at the switch or module
- Failed recline switch (internal contact failure)
- Faulty seat control module / BCM input circuit
- Blown fuse or loss of power/ground to the switch
- Water intrusion or mechanical damage in the seat harness
Symptoms
- Driver seat will not recline rearward when switch is pressed
- Seat may not respond or responds intermittently to recline rearward input
- DTC B1820 stored in body/seat control module
- Other seat functions may be unaffected (forward, tilt) or multiple seat-related codes present
- Possible blown fuse for seat circuits
What to check
- Retrieve stored codes and freeze-frame data with a scan tool; note any related seat or BCM codes
- Perform a visual inspection of the driver seat harness, connectors, and switch for damage, corrosion, or water intrusion
- Check relevant fuses and relays for the seat power circuit
- Backprobe the recline switch connector and monitor voltage or continuity while actuating the switch
- Wiggle the harness and operate the switch to reproduce the fault and check for intermittent behavior
- Measure continuity between the switch connector and the seat control module/BCM input pin with connectors disconnected
Signal parameters
- Supply voltage at switch: ~11–14 V (battery voltage) on the power feed when circuit is powered
- Ground reference: near 0 V at chassis ground and switch ground pin
- Switch closed continuity: near 0–2 ohms between signal and ground (or continuity according to factory spec)
- Switch open: infinite resistance (open circuit) on the switched path
- Signal line behavior: toggles between battery voltage and open (or between ~0 V and ~5 V) depending on system design — confirm with factory wiring diagram
- If monitored by module: switch state should change in scan tool live data when actuator is pressed
Diagnostic algorithm
- Connect a diagnostic scan tool and record B1820 and any related codes; view live data for recline switch state.
- Visually inspect the driver seat, switch assembly, and wiring harness for damage, chafing, or corrosion; repair obvious damage.
- Check fuses/relays for the seat circuit; replace if blown and retest. If fuse blows repeatedly, suspect short.
- Backprobe the recline switch connector with the ignition ON. Confirm there is proper supply voltage and ground at the switch per the wiring diagram.
- Operate the rearward recline switch while observing the signal line with a multimeter or oscilloscope. Verify the signal changes state (open/closed or voltage change) as expected.
- If no correct signal at the switch, disconnect the switch and measure continuity across the switch terminals while actuating. Replace switch if it does not change state correctly.
- If switch tests good, check continuity from the switch signal pin to the module input pin. Repair any open or high-resistance wiring or connector terminals.
- If short to ground or battery is suspected, isolate sections of the harness to locate the short and repair/replace damaged wiring.
- After repairs, clear codes and verify proper operation of the recline rearward function and that B1820 does not return. Re-check with full seat travel and wiggle test.
- If wiring and switch are good but the code persists, consider module input circuit fault; inspect module connector pins and update or replace module only after wiring and switch are confirmed good.
Likely causes
- Broken wire or pinched harness where it passes through the seat frame or door sill
- Corroded or loose connector at the recline switch or module
- Failed rearward recline switch contact (worn or stuck)
- Short to ground or short to battery on the switch signal wire
- Connector terminal pushed out or bent
- Intermittent open caused by repeated seat movement or seat belt retractor interference
Fault status
Status
Driver seat rearward recline switch circuit malfunction detected. Seat may not recline rearward.
Repair difficulty: Medium
Diagnostic time: 0.8-2.0 hours
Similar codes
Repair manuals
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138
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Code
B1820
Other
B — Body
Wiper Rear Motor Up Relay Coil Circuit Short To Battery
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the recline switch circuit
- Poor or corroded connector or terminal at the switch or module
- Failed recline switch (internal contact failure)
- Faulty seat control module / BCM input circuit
- Blown fuse or loss of power/ground to the switch
- Water intrusion or mechanical damage in the seat harness
Symptoms
- Driver seat will not recline rearward when switch is pressed
- Seat may not respond or responds intermittently to recline rearward input
- DTC B1820 stored in body/seat control module
- Other seat functions may be unaffected (forward, tilt) or multiple seat-related codes present
- Possible blown fuse for seat circuits
What to check
- Retrieve stored codes and freeze-frame data with a scan tool; note any related seat or BCM codes
- Perform a visual inspection of the driver seat harness, connectors, and switch for damage, corrosion, or water intrusion
- Check relevant fuses and relays for the seat power circuit
- Backprobe the recline switch connector and monitor voltage or continuity while actuating the switch
- Wiggle the harness and operate the switch to reproduce the fault and check for intermittent behavior
- Measure continuity between the switch connector and the seat control module/BCM input pin with connectors disconnected
Signal parameters
- Supply voltage at switch: ~11–14 V (battery voltage) on the power feed when circuit is powered
- Ground reference: near 0 V at chassis ground and switch ground pin
- Switch closed continuity: near 0–2 ohms between signal and ground (or continuity according to factory spec)
- Switch open: infinite resistance (open circuit) on the switched path
- Signal line behavior: toggles between battery voltage and open (or between ~0 V and ~5 V) depending on system design — confirm with factory wiring diagram
- If monitored by module: switch state should change in scan tool live data when actuator is pressed
Diagnostic algorithm
- Connect a diagnostic scan tool and record B1820 and any related codes; view live data for recline switch state.
- Visually inspect the driver seat, switch assembly, and wiring harness for damage, chafing, or corrosion; repair obvious damage.
- Check fuses/relays for the seat circuit; replace if blown and retest. If fuse blows repeatedly, suspect short.
- Backprobe the recline switch connector with the ignition ON. Confirm there is proper supply voltage and ground at the switch per the wiring diagram.
- Operate the rearward recline switch while observing the signal line with a multimeter or oscilloscope. Verify the signal changes state (open/closed or voltage change) as expected.
- If no correct signal at the switch, disconnect the switch and measure continuity across the switch terminals while actuating. Replace switch if it does not change state correctly.
- If switch tests good, check continuity from the switch signal pin to the module input pin. Repair any open or high-resistance wiring or connector terminals.
- If short to ground or battery is suspected, isolate sections of the harness to locate the short and repair/replace damaged wiring.
- After repairs, clear codes and verify proper operation of the recline rearward function and that B1820 does not return. Re-check with full seat travel and wiggle test.
- If wiring and switch are good but the code persists, consider module input circuit fault; inspect module connector pins and update or replace module only after wiring and switch are confirmed good.
Likely causes
- Broken wire or pinched harness where it passes through the seat frame or door sill
- Corroded or loose connector at the recline switch or module
- Failed rearward recline switch contact (worn or stuck)
- Short to ground or short to battery on the switch signal wire
- Connector terminal pushed out or bent
- Intermittent open caused by repeated seat movement or seat belt retractor interference
Fault status
Status
Driver seat rearward recline switch circuit malfunction detected. Seat may not recline rearward.
Repair difficulty: Medium
Diagnostic time: 0.8-2.0 hours
Similar codes
Repair manuals
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