P0512

Code

Generic P — Powertrain

Starter Request Circuit

Brand: Generic

Type: P — Powertrain

Views: UK: 25 EN: 36 RU: 41

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or short in starter request wiring
Failed starter relay or relay socket
Faulty ignition switch or key switch contacts
Poor connector contact or corrosion at relay, starter solenoid or module
Weak or discharged battery or poor battery terminals/ground
Intermittent wiring damage (chafing, pinched, broken strands)

Symptoms

No-crank (key to START produces no starter action)
Intermittent crank/no-crank condition
Starter engages without key or unexpected cranking (rare)
No change in starter request signal when turning key
Possible illuminated MIL or security lamp

What to check

Scan for stored/active codes and freeze-frame data; note key status and battery voltage
Measure battery resting and cranking voltage; verify good battery terminals and ground
Visually inspect fuses, fusible links and starter relay; swap known-good relay if available
Inspect starter, solenoid and relay connectors for corrosion, heat damage, loose pins
Backprobe starter request wire at relay/PCM while actuating START; observe voltage behavior
Wiggle test wiring harness while cranking to reproduce intermittent failures

Signal parameters

Rest (no start): starter request circuit ≈ 0 V (or low) relative to battery negative
Cranking (key START): starter request circuit ≈ battery voltage (~9–14 V) when driver requests starter
Intermittent signal: erratic/noisy voltage, rapid drop under load, or pulsed output
Continuity: low resistance path between ignition switch, relay coil, and PCM/BCM input when measured per service manual

Diagnostic algorithm

Retrieve codes and live data; note battery voltage and starter request status during attempt to start.
Verify battery condition and clean/tighten battery terminals and main grounds. Re-check code after restoring proper battery connections.
Inspect relevant fuses, fusible links and the starter relay. Swap relay with identical known-good relay to quickly test.
Backprobe the starter request/command wire at the relay coil or PCM input. With helper turning key to START, observe voltage and behavior. Expect ~battery voltage during crank, ~0 V otherwise.
If request voltage is absent, trace wiring back to ignition switch and PCM. Check for opens/shorts to power or ground and poor connector pins. Repair or replace damaged wiring/connectors.
If request voltage is present at relay but starter does not operate, check relay output to starter solenoid and measure voltage at starter solenoid terminal during crank. If voltage present but starter does not engage, investigate starter/solenoid.
If intermittent signal or noisy voltage is found, perform wiggle tests along harness and repair wiring harness chafe or broken wires.
If wiring and starter/relay check good, test or substitute PCM/BCM driver per manufacturer procedures; check immobilizer module/antitheft inhibit circuits and key programming as applicable.
After repairs, clear codes, perform multiple start attempts and road test to confirm repair. Re-scan for codes and monitor live data.

Likely causes

Corroded/loose connector at starter relay or starter solenoid
Open wire between ignition switch and starter relay/PCM
Stuck or failed starter relay coil
Low battery voltage causing erroneous signal
Ground loss at starter or chassis ground strap

Fault status

⚠️ Status

Starter Request Circuit fault — open, short, intermittent or out-of-range voltage detected on the starter request/command circuit. Inspect wiring, relay, ignition switch, battery and control module.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours