Code
P1623
DAEWOO
P — Powertrain
Mil open / short
AI status
Completed
Completed
100%
Causes
- Burned out or faulty MIL/indicator bulb (or LED cluster)
- Blown fuse or fusible link related to instrument cluster/ECU power
- Damaged wiring harness (open, short to ground, or short to battery) on MIL lamp circuit
- Corroded/loose connectors at instrument cluster, ECM/BCM or ground points
- Faulty instrument cluster (lamp driver) or faulty ECU/BCM output stage
- Incorrect replacement parts (wrong bulb type or LED retrofit)
Symptoms
- MIL (Check Engine Light) does not illuminate with ignition ON (self-test)
- MIL remains permanently ON or flickers intermittently
- DTC stored on BCM/ECM referencing MIL circuit open/short
- Possible loss of diagnostics readiness indication on cluster
- Intermittent or no communication with instrument cluster in some cases
What to check
- Use a scan tool to confirm P1623 is current or stored and note freeze-frame/related codes
- Visually inspect MIL lamp/bulb or indicator cluster for damage or modification
- Check fuses and fusible links for the instrument cluster and ECM/BCM power circuits
- Inspect wiring and connectors between ECM/BCM and instrument cluster for corrosion, pin damage, or disconnected terminals
- Verify battery voltage is stable (12–14 V) before electrical tests
- Backprobe MIL circuit connector at the ECU/BCM and at the cluster while observing connector pins for corrosion or bent pins
Signal parameters
- With ignition ON (key ON, engine OFF) the MIL circuit should allow lamp self-test: cluster lamp sees battery voltage (≈12 V) through lamp until ECU momentarily drives the circuit to illuminate the lamp
- When ECU/BCM drives the MIL lamp the lamp circuit is typically pulled toward ground (near 0 V) or switched to ground; verify expected voltage by backprobing (values depend on vehicle and lamp type)
- Open-circuit: very high resistance or infinite ohms between MIL terminal at cluster and ECU/BCM pin
- Short-to-ground: near 0 Ω between MIL feed and chassis ground; short-to-battery: near 0 Ω between MIL feed and battery positive
- Lamp current for filament bulbs typically hundreds of mA; LED indicators draw much less — check expected current in vehicle documentation
Diagnostic algorithm
- Connect a capable scan tool, confirm P1623 and record related codes and freeze frame data. Do not immediately replace modules based on code alone.
- Visually inspect instrument cluster lens/assembly and MIL bulb/LED installation for damage or aftermarket changes. Check cluster fuse(s).
- With ignition OFF, disconnect connectors at instrument cluster and ECU/BCM. Inspect pins for corrosion, damage, or pushed-out terminals.
- Check continuity/resistance between the MIL lamp pin at the cluster and the MIL output pin at the ECU/BCM. Expect low resistance through the lamp circuit (unless the lamp is removed). High/infinite resistance indicates open wiring or connector fault.
- With ignition ON, backprobe the MIL output pin at the ECU/BCM and the cluster MIL feed. Observe voltages: verify battery presence, and that the ECU toggles the line during key-on self-test. No toggling suggests ECU/cluster driver or wiring fault.
- Check for short to ground or battery: with ignition OFF check resistance from MIL feed to ground and to battery positive. Low resistance to either indicates a short.
- If wiring and connectors test good, bench-test or swap a known-good instrument cluster (if available) before replacing ECU/BCM. Confirm whether lamp driver in cluster or module output is faulty.
- Repair or replace damaged wiring/connectors, replace burned-out bulb/cluster, or only replace module after verifying module output failure. Clear codes and perform driving cycle to confirm repair.
- If module replacement is required, follow vehicle manufacturer programming and immobilizer/security procedures as applicable.
Likely causes
- Open or corroded connector at instrument cluster or ECM/BCM
- Broken wire between instrument cluster MIL terminal and ECU/BCM
- Failed instrument cluster lamp driver (common on clusters with integrated LEDs)
- Blown fuse supplying the cluster or ECU
Fault status
Status
MIL circuit open or short detected — check instrument cluster lamp, wiring, fuses, grounds, and ECU/BCM output before replacing modules.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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