Code
B1805
HUMMER
B — Body
Ignition Switch Problem
AI status
Completed
Completed
100%
Causes
- Failed/dirty ignition switch contacts or internal switch assembly failure
- Damaged, chafed or shorted wiring in ignition switch harness
- Corroded/loose connector(s) at ignition switch or body control module (BCM)
- Blown fuse or faulty relay supplying ignition circuits
- Poor ground at instrument panel/BCM grounds
- Faulty BCM or input circuitry
Symptoms
- No crank or intermittent crank condition
- Accessories (radio, power outlets) do not power in key ACC/RUN positions
- Instrument cluster or dash indicators flicker or show incorrect ignition position
- Starter does not engage when key turned to START position
- Key may feel loose or stick in cylinder
- Malfunction indicator or security/anti-theft lamp illuminated
What to check
- Read all stored codes and freeze frame data from BCM and other modules; record ignition-related data
- Check battery state-of-charge and charging system (low voltage can cause false faults)
- Inspect fuses and relays for ignition/ACC circuits (replace as needed)
- Visually inspect ignition switch connector and wiring harness for damage, corrosion, loose pins, or aftermarket splices
- Backprobe ignition switch connector and measure voltages in each key position (OFF/ACC/RUN/START)
- Wiggle test wiring/connectors while observing scan tool data or ignition-related symptoms
Signal parameters
- Battery voltage (static): ~12.4–12.8 V (vehicle off, fully charged)
- Battery voltage (engine running): ~13.5–14.8 V
- ACC terminal: near battery voltage when key in ACC, ~0 V when off
- RUN/IGN terminal(s): near battery voltage when key in RUN, ~0 V when off
- START terminal: battery voltage only while cranking (momentary)
- Closed-circuit continuity on switch contacts: typically >1 kΩ)
Diagnostic algorithm
- Connect a professional scan tool; retrieve/record B1805 and any related codes from BCM and other modules. Note ignition position data and any freeze-frame values.
- Verify battery voltage and cranking voltage. Charge or replace battery if low; recheck code. Low voltage can produce false ignition-switch faults.
- Inspect fuses and relays for the ignition/ACC circuits. Replace suspect items and re-test.
- Visually inspect ignition switch connector under dash for corrosion, pushed-out pins, or aftermarket splices. Repair as required.
- Backprobe ignition switch harness terminals. With key in OFF, ACC, RUN, and while cranking, measure voltage at ACC, RUN, and START circuits and compare to expected signal_params. Verify START terminal only has voltage during cranking.
- Check continuity from the ignition switch pins to the BCM/relay harness while moving the steering column and key cylinder (look for intermittent opens).
- Perform wiggle test on wiring and connector while monitoring scan tool live data (ignition position bits) or observing symptom reproduction.
- If wiring and connector checks are good but signals remain incorrect, check BCM input circuits and grounds. If BCM inputs are faulty and wiring is verified good, consider BCM repair/replacement per manufacturer procedures.
- If ignition switch shows internal failure (incorrect voltages/continuity), remove and replace the ignition switch assembly or lock cylinder per vehicle service manual. Reprogram/learn procedures if required.
- Clear codes and perform road test/functional test. Confirm fault does not return and ignition positions are correctly reported.
Likely causes
- Worn internal ignition switch contacts causing intermittent loss of ACC/RUN/START signals
- Corroded connector or bent terminal at ignition switch harness
- Broken or pinched wire between ignition switch and BCM or starter relay
- Blown ignition fuse or failing starter/ignition relay
Fault status
Status
Ignition switch circuit fault detected — ignition position/input signals inconsistent or missing.
Repair difficulty: Medium
Diagnostic time: 0.5 - 2.0 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
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Code
B1805
Other
B — Body
Lamp Turn Signal Rear Output Circuit Short To Ground
AI status
Completed
Completed
100%
Causes
- Failed/dirty ignition switch contacts or internal switch assembly failure
- Damaged, chafed or shorted wiring in ignition switch harness
- Corroded/loose connector(s) at ignition switch or body control module (BCM)
- Blown fuse or faulty relay supplying ignition circuits
- Poor ground at instrument panel/BCM grounds
- Faulty BCM or input circuitry
Symptoms
- No crank or intermittent crank condition
- Accessories (radio, power outlets) do not power in key ACC/RUN positions
- Instrument cluster or dash indicators flicker or show incorrect ignition position
- Starter does not engage when key turned to START position
- Key may feel loose or stick in cylinder
- Malfunction indicator or security/anti-theft lamp illuminated
What to check
- Read all stored codes and freeze frame data from BCM and other modules; record ignition-related data
- Check battery state-of-charge and charging system (low voltage can cause false faults)
- Inspect fuses and relays for ignition/ACC circuits (replace as needed)
- Visually inspect ignition switch connector and wiring harness for damage, corrosion, loose pins, or aftermarket splices
- Backprobe ignition switch connector and measure voltages in each key position (OFF/ACC/RUN/START)
- Wiggle test wiring/connectors while observing scan tool data or ignition-related symptoms
Signal parameters
- Battery voltage (static): ~12.4–12.8 V (vehicle off, fully charged)
- Battery voltage (engine running): ~13.5–14.8 V
- ACC terminal: near battery voltage when key in ACC, ~0 V when off
- RUN/IGN terminal(s): near battery voltage when key in RUN, ~0 V when off
- START terminal: battery voltage only while cranking (momentary)
- Closed-circuit continuity on switch contacts: typically >1 kΩ)
Diagnostic algorithm
- Connect a professional scan tool; retrieve/record B1805 and any related codes from BCM and other modules. Note ignition position data and any freeze-frame values.
- Verify battery voltage and cranking voltage. Charge or replace battery if low; recheck code. Low voltage can produce false ignition-switch faults.
- Inspect fuses and relays for the ignition/ACC circuits. Replace suspect items and re-test.
- Visually inspect ignition switch connector under dash for corrosion, pushed-out pins, or aftermarket splices. Repair as required.
- Backprobe ignition switch harness terminals. With key in OFF, ACC, RUN, and while cranking, measure voltage at ACC, RUN, and START circuits and compare to expected signal_params. Verify START terminal only has voltage during cranking.
- Check continuity from the ignition switch pins to the BCM/relay harness while moving the steering column and key cylinder (look for intermittent opens).
- Perform wiggle test on wiring and connector while monitoring scan tool live data (ignition position bits) or observing symptom reproduction.
- If wiring and connector checks are good but signals remain incorrect, check BCM input circuits and grounds. If BCM inputs are faulty and wiring is verified good, consider BCM repair/replacement per manufacturer procedures.
- If ignition switch shows internal failure (incorrect voltages/continuity), remove and replace the ignition switch assembly or lock cylinder per vehicle service manual. Reprogram/learn procedures if required.
- Clear codes and perform road test/functional test. Confirm fault does not return and ignition positions are correctly reported.
Likely causes
- Worn internal ignition switch contacts causing intermittent loss of ACC/RUN/START signals
- Corroded connector or bent terminal at ignition switch harness
- Broken or pinched wire between ignition switch and BCM or starter relay
- Blown ignition fuse or failing starter/ignition relay
Fault status
Status
Ignition switch circuit fault detected — ignition position/input signals inconsistent or missing.
Repair difficulty: Medium
Diagnostic time: 0.5 - 2.0 hours
Similar codes
Repair manuals
Brands with available manuals
9,587
The library contains 9,587 repair and diagnostic manuals. Choose a brand to open the full manual tree by year, model and trim.
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