P2AF9

Code

Generic P — Powertrain

Starter Relay D Control Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 21 EN: 51 RU: 27

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Page language: EN

Causes

Open or damaged relay ground or control wiring
Short to battery voltage on the relay control circuit
Faulty starter relay (stuck closed or internally shorted)
Faulty PCM/BCM driver transistor or module output
Corroded/loose connector or poor pin contact at relay socket or module
Aftermarket accessory (remote starter, alarm) backfeeding the circuit

Symptoms

Starter does not operate or intermittent cranking
Starter engages without key or crank signal (possible stuck relay)
No crank when start commanded and starter relay control shows abnormal voltage
Blown fuses or parasitic battery drain
Malfunction indicator or other modules reporting related errors

What to check

Scan tool: read live data for starter relay D command and status; attempt to command relay and observe response
Visually inspect relay, socket, wiring harness, and connectors for damage, corrosion, or pin push-out
Measure battery voltage to verify system voltage is within 11–15 V range
Backprobe relay control pin and compare voltage with scan tool command (key ON and START)
Remove relay and measure coil resistance with multimeter
Check continuity between relay control pin and PCM/BCM output and to ground as applicable

Signal parameters

Typical expected behavior (generic): control circuit should switch between near 0–1 V (driver pulled low/ground when activated) and near battery voltage (11–14.5 V) when released. Exact polarity depends on vehicle (low-side vs high-side driver).
Relay coil resistance (typical range): 50–200 ohms (varies by relay).
When commanded ON by module, control pin should change state within 0.1–0.5 s of command.
Measured voltage significantly above expected when circuit is supposed to be low indicates a ‘control circuit high’ fault.

Diagnostic algorithm

Record freeze frame and stored data with scan tool; note conditions when code set.
Verify battery voltage and terminal condition before testing.
With ignition OFF, visually inspect relay, socket, wiring, and connectors for damage or corrosion; repair as needed.
Use a scan tool to command Starter Relay D ON/OFF while monitoring the control circuit voltage at the relay socket (backprobe). Note voltages with command ON and OFF.
If control circuit is high when commanded low, remove relay and measure coil resistance. If coil shorted/low resistance, replace relay and retest.
If relay coil is normal, disconnect relay harness and measure voltage at PCM/BCM output with harness disconnected while commanding relay. If voltage is still high, suspect PCM/BCM driver fault.
Check wiring continuity between PCM/BCM and relay socket; check for short to battery (measure resistance to B+ with battery disconnected).
Inspect for aftermarket modules that may be backfeeding the circuit; disconnect temporarily to test.
If wiring and relay are good but problem persists, consult vehicle-specific service data for PCM/BCM output testing and consider replacing module only after verification.
Clear codes and perform functional test (start/command cycles) to confirm repair; monitor for recurrence.

Likely causes

Short to battery (wire chafed and contacting +12V) on control lead
Failed starter relay with internal short
Corroded connector at relay socket causing incorrect readings
Faulty/shorted output stage in PCM/BCM driving the relay

Fault status

⚠️ Status

Starter Relay D Control Circuit High — control circuit voltage exceeded the permitted threshold; stored when PCM/BCM detects a high voltage condition on the relay control output.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours