Code
B2420
HUMMER
B — Body
Twilight Delay Pot Failure
AI status
Completed
Completed
100%
Causes
- Failed or worn Twilight Delay potentiometer (variable resistor).
- Open or short in the potentiometer signal, reference, or ground wiring.
- Poor connector contact or corrosion at the potentiometer connector.
- Incorrect reference voltage or bad ground at the BCM.
- Faulty BCM or internal input circuit failure.
- Aftermarket modifications or water ingress damaging the sensor or wiring.
Symptoms
- Fault code B2420 stored and possibly MIL or body warning lamps.
- Twilight/delay feature inoperative or behaves inconsistently (lights not delaying or wrong timing).
- Intermittent operation of related lighting functions.
- Possible erratic readings shown by scan tool when operating the control.
What to check
- Retrieve freeze frame and current data with a scan tool; confirm DTC and any related codes.
- Visually inspect the potentiometer, harness, and connector for damage, corrosion, or water intrusion.
- Perform a wiggle test on the wiring/connectors while monitoring the signal with a scan tool or DVOM.
- Verify reference voltage and ground at the potentiometer connector with key ON (consult service manual for exact pins).
- Measure potentiometer signal voltage while operating the control — expect a variable voltage (typically within 0–5 V range) or changing resistance per OEM spec.
- Check for related BCM codes that may indicate module issues.
Signal parameters
- Reference supply: typically an ignition-switched 5 V reference (consult factory data for exact value).
- Signal: variable voltage proportional to pot position — should move smoothly when control is adjusted (commonly 0.2–4.8 V range).
- Ground: solid chassis or BCM ground with near 0 Ω continuity to battery negative (verify).
- Resistance: pot should show smooth, continuous change in resistance across its travel (check with ohmmeter against spec).
- No rapid voltage spikes or complete loss of signal when operating control.
Diagnostic algorithm
- Read and record all codes and freeze-frame data; note whether code is current, pending, or historical.
- Visually inspect potentiometer assembly, connector, and wiring for damage, corrosion, or moisture; repair obvious issues.
- Backprobe connector with key ON and measure reference voltage and ground continuity. Compare to factory values. If reference or ground missing, trace/fix wiring to ECM/BCM or power/ground source.
- Measure the potentiometer signal voltage while operating the control; verify smooth change. If signal is absent, stuck, or erratic, check for opens/shorts between pot and BCM.
- If signal wiring checks good, measure pot resistance directly (disconnect connector). Confirm resistance varies smoothly across travel and within spec. Replace pot if out of spec or noisy.
- If wiring and pot are good but signal not seen at BCM input, perform continuity and shorts-to-power/ground tests on harness. Repair any faults.
- If harness and sensor are good and correct signals are present at the BCM connector but the code remains, consider BCM software update or module diagnosis/ replacement per factory procedures.
- After repairs clear codes and verify proper function and that code does not return under normal operating conditions.
Likely causes
- Corroded/loose connector at the potentiometer (most common).
- Failed potentiometer (mechanical wear or internal short).
- Broken or chafed harness causing intermittent/short to power or ground.
- BCM input circuit fault (least common).
Fault status
Status
Twilight Delay Potentiometer circuit fault — signal out of range/open/short
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
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