Code
B2790
Generic
B — Body
Starter Relay Circuit Malfunction
Views:
UK: 6
EN: 5
RU: 4
AI status
Completed
Completed
100%
Causes
- Faulty starter relay (stuck, welded contacts, internal open)
- Blown fuse or fusible link in starter/control circuit
- Open, shorted or corroded wiring/connectors between battery, relay, starter and control module
- Poor or missing ground at relay or starter
- Faulty ignition switch or starter control output from BCM/PCM
- Intermittent connection or water ingress in relay/socket
Symptoms
- No-crank condition (key turned but starter does not engage)
- Intermittent starting or inconsistent starter engagement
- Clicking sound from relay area when key is turned
- No voltage present at starter control terminal when commanded
- Possible dashboard warning lamps or immobilizer/anti-theft messages
- Battery draining if relay stuck closed
What to check
- Verify battery state of charge and battery terminal connections
- Scan for present and pending codes, read freeze frame and data
- Visually inspect relay, fuse, fusible links, and connector for damage or corrosion
- Measure voltage at relay coil input and coil ground while commanding starter
- Check continuity and resistance of wiring between relay, starter and control module
- Wiggle test wiring and connectors to reproduce intermittent faults
Signal parameters
- Battery voltage at relay power terminal: ~12.4–12.8 V (engine off, good battery)
- Command signal voltage from ignition/BCM to relay coil: approx. 0–12 V (should go high/low per vehicle design) when cranking
- Coil resistance (relay dependent): typically 50–200 ohms for small control relays (refer to service data)
- Starter solenoid control terminal voltage when cranking: near battery voltage if commanded
- No-load current when coil energized: varies by relay — measure against spec
Diagnostic algorithm
- Safety first: Park vehicle, apply parking brake, wear eye protection, and block wheels. Disconnect battery only if required by procedures.
- Verify battery voltage and reset codes. Ensure battery >=12.4 V for tests.
- Scan modules, note B2790 and any related codes (starter, BCM, immobilizer). Check freeze frame and live data while attempting start.
- Inspect fuses/fusible links for starter/relay circuits. Replace any blown items and re-test.
- Locate starter relay and socket. Visually inspect for corrosion, heat damage, or loose terminals. Replace relay with known-good identical relay and retest starting.
- Backprobe relay power and control terminals. With key turned to START, observe/control signal: verify battery feed is present and control signal changes as commanded.
- If control signal absent, trace back to ignition switch/BCM: check for commands from BCM with a scan tool and verify wiring continuity between BCM and relay.
- Check ground circuits: measure voltage drop between ground points while cranking. Repair poor grounds as necessary.
- Bench-test suspect relay for coil resistance and switching operation or swap with an identical known-good relay in vehicle (if available).
- Inspect wiring harness between relay and starter for shorts to ground or open circuits. Repair any damaged wiring or connectors.
- If wiring and relay are good but command remains abnormal, test BCM/PCM output driver pin for shorts to power/ground. Replace module only after excluding wiring and relay faults.
- After repairs, clear codes, attempt multiple start cycles and re-scan to confirm B2790 does not return.
Likely causes
- Corroded relay socket or connector causing intermittent contact
- Open or high-resistance ground or power feed to relay coil
- Failed starter relay
- Damaged wiring harness near starter or relay (chafing, rodent damage)
- Faulty BCM/PCM output driver for starter relay
Fault status
Status
Starter relay circuit malfunction detected — control module observed abnormal starter relay behavior (open/short/intermittent). May cause no-crank or intermittent starting. Further electrical diagnosis required.
Repair difficulty: Medium
Diagnostic time: 1-2 hours
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