P1631

Code

Other P — Powertrain

Theft Deterrent Start Enable Signal Not Correct/ Main Relay Malfunction (Power Hold)

Brand: Other

Type: P — Powertrain

Views: UK: 44 EN: 290 RU: 63

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Page language: EN

No-crank or no-start condition (starter disabled or engine stalls shortly after start)
Starter relay/solenoid may click but engine does not start
Intermittent starting or start works only with key/ignition cycling
Theft/immobilizer warning lamp illuminated or flashing
Other powered engine control modules losing power or rebooting

Read and record all stored codes and freeze frame data; note related theft/immobilizer codes
Check battery voltage and terminals; confirm battery is fully charged
Inspect fuses and fusible links for the main relay, ECU/PCM power circuits and theft module
Locate and visually inspect the main relay and associated connectors for corrosion or damage
Observe theft/immobilizer indicator behavior with key insertion/turn-on
Backprobe relay coil and switched output with scan tool or DVOM while cranking/trying to start

Battery voltage: ~12.6 V at rest, >=9 V during cranking (should not be extremely low)
Start Enable signal (from immobilizer/BCM to PCM): inactive ~0 V, active ~12 V (or logic-high per vehicle spec)
Main relay control coil: coil resistance typically 50–200 ohms (varies by relay); coil should see ~12 V when energized
Main relay switched output (power-hold): ~12 V present to ECU/main power bus when relay is latched
Starter control feed: 12 V present at starter solenoid when start-enable is active and key at crank

Record all codes and freeze-frame; clear codes and attempt to re-create the fault while monitoring data and theft indicator.
Verify battery condition and charge; clean and tighten battery terminals. Low voltage can cause control module/relay faults.
Inspect and verify fuses/fusible links for main relay, ECM/BCM and theft deterrent supply. Replace any blown fuses.
Locate main relay. Inspect connector for corrosion, bent pins, burnt terminals. With connector disconnected, check relay pins for continuity and coil resistance against relay spec.
Backprobe the relay connector while attempting to start: verify coil supply voltage and ground, and that the switched output provides 12 V when activated.
If relay input has 12 V but relay does not switch, bench-test or replace the relay and retest.
Monitor the start-enable signal from the immobilizer/BCM to the PCM using a scan tool or DVOM. If no enable is issued, check immobilizer wiring and key transponder recognition.
Check grounds for ECM/BCM and related modules; measure voltage drops under load on main power and ground circuits.
Repair any damaged wiring or connectors found. After repairs, clear codes and verify normal operation through several start cycles.
If wiring, relays and immobilizer key checks are good but fault persists, investigate module outputs (BCM/ECM drive circuits) and consider professional module diagnosis or replacement.