P2AF2

Code

Generic P — Powertrain

Starter Relay C Control Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 15 EN: 32 RU: 18

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Page language: EN

Causes

Open or high-resistance wiring between the control module and starter relay C
Faulty starter relay (coil open)
Blown fuse or fusible link supplying the relay/coil circuit
Poor or corroded connector at the relay, ground, or control module
Failed control module (BCM/PCM) output transistor
Aftermarket alarm/immobilizer or recent wiring modification interfering with circuit

Symptoms

No-crank condition when key or start request issued
No audible relay click from starter relay location
Intermittent starting or starts only when tapping relay/connector
Starter does not engage even though other systems have power
Related instrument cluster messages or immobilizer warnings (depending on vehicle)

What to check

Verify battery voltage is healthy (12.4 V+ at rest, >10 V while cranking)
Inspect starter and ignition fuses, fusible links, and relay sockets
Listen at relay location for click while attempting to start
Visually inspect relay connector and wiring for corrosion, damage, or loose pins
Scan for other related DTCs and freeze-frame data before clearing codes

Signal parameters

Relay coil resistance: typically ~50–200 ohms (refer to vehicle spec); open = infinite ohms
Control module output: logic/driver energized on crank — expect ~battery voltage at relay control terminal when activated
Inactive control: near 0 V or module-specific pulled-high/low state (check vehicle wiring diagram)
Allowed voltage drop on control line: under ~0.5 V under expected load (excessive drop indicates high resistance)
Continuity expected between module control pin and relay coil control terminal (low ohms); open = no continuity

Diagnostic algorithm

Retrieve freeze frame and permanent/fault history. Note whether code is current or intermittent and conditions (key position, engine temp, battery voltage).
Check battery condition and charge to rule out low-voltage false readings.
Inspect fuses and fusible links related to starter/relay circuits. Replace any blown fuses and re-check code.
Perform a visual inspection of the starter relay, its socket, and wiring harness for corrosion, damaged insulation, or loose terminals.
With ignition off, remove relay and measure coil resistance across relay coil terminals. If coil reads open (infinite), replace relay.
Check for continuity between the control module’s relay-control pin and the relay socket control terminal. Repair any open or high-resistance wiring.
With a helper turning the key to START (or using a safe remote crank request), measure voltage at the relay control terminal. Confirm the control module is commanding (voltage present) when cranking.
If no command voltage is present, back-probe the module output pin and inspect for ground/driver faults. Compare against wiring diagram to determine if driver is ground-switching or supply-switching.
Check ground points and supply voltage to the relay coil. Repair poor grounds or supply feed issues.
If wiring, connectors, fuse and relay are good but no control signal, suspect control module driver fault. Verify with manufacturer diagnostics before replacing module.
After repairs, clear codes, perform repeated start attempts, and confirm code does not return. Road test and re-scan to verify repair.

Likely causes

Broken or chafed wire in harness to starter relay coil
Relay coil internal open
Blown fuse in starter/relay feed or ignition fuse
Corroded connector or pin pushed out at the relay
Faulty module driver (open output) in BCM/PCM

Fault status

⚠️ Status

Starter Relay C control circuit open: control module did not detect the expected control signal to the starter relay (open circuit or no command). Check relay, wiring, fuses, grounds and control module output.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours