Code
P1280
JEEP
P — Powertrain
Open Or Shorted Condition Detected In The Fuel System Relay Control Circuit
AI status
Completed
Completed
100%
Causes
- Blown fuse for fuel pump/fuel system relay circuit
- Faulty fuel pump relay (stuck open or internal short)
- Damaged wiring (open, short to ground, short to battery) in relay control or supply circuit
- Corroded/poor connector or terminal at relay, fuse, or PCM
- Faulty PCM or relay drive transistor (rare)
- Aftermarket accessories or recent repairs that disturbed wiring
Symptoms
- Engine cranks but won’t start (no fuel pressure)
- Intermittent starts or stalls
- No fuel pump operation when key-on or engine cranking
- Fuel pump runs continuously in some cases
- Related MIL illumination and stored DTC P1280
What to check
- Read freeze frame and stored data with a scan tool; note ignition/key status when code set
- Visually inspect fuse(s) and relay(s) for the fuel pump/fuel system; check for blown fuse and damaged relay
- Inspect wiring and connectors at the relay, fuse block, fuel pump, and PCM for corrosion, pin damage, loose terminals, or melted insulation
- With ignition ON (engine off) command the fuel pump relay on/off with a scan tool and listen for relay clicking or pump operation
- Measure battery voltage at the relay power feed and at the relay control pin while commanding ON/OFF
- Check for stored or pending codes that indicate low/high system voltage (which can affect relay operation)
Signal parameters
- Battery supply to relay power terminal: approximately battery voltage (approx. 11–14.5 V) with key ON
- Relay coil/control circuit: expected logic when PCM is driver-type — typically 0–0.5 V when PCM grounds the control (relay energized), and near battery voltage when not energized (open)
- Control circuit resistance: open circuit indicated by very high resistance or infinite ohms between PCM control pin and relay coil ground side; short to ground indicated by near 0 ohms to chassis ground
- Relay coil current (typical): tens to a few hundred milliamps (depends on relay)
Diagnostic algorithm
- Verify complaint and record conditions when DTC set using a scan tool (freeze frame, ignition state).
- Step 1 — Visual and basic checks: inspect fuses, relay, and connectors for damage or corrosion. Replace fuse if blown and check immediately if it blows again.
- Step 2 — Verify relay operation: swap with a known-good identical relay (same part number) or bench-test relay. If swapping cures the fault, replace the relay.
- Step 3 — Check power feed: with ignition ON, measure battery voltage at relay power terminal. If absent, trace and repair feed fuse, fusible link, or wiring to battery or ignition switch.
- Step 4 — Check control/trigger circuit: backprobe the relay control terminal and command the relay ON with a scan tool. Verify the control voltage switches between ~battery voltage and ~0 V (or vice versa depending on design). If control never changes, test wiring continuity from relay to PCM and inspect connector pins.
- Step 5 — Check for shorts: with ignition OFF, measure resistance between the control circuit and chassis ground and between the control circuit and battery positive to identify short to ground or short to battery. Repair wiring as needed.
- Step 6 — Test PCM driver: if wiring and relay are good but control circuit behaves incorrectly, test or swap PCM per factory procedure or consult OEM tech data. Consider professional ECU testing/repair.
- Step 7 — After repairs: clear codes, perform key cycle and cranking tests, verify fuel pump operation and fuel pressure, and road test to confirm code does not return.
Likely causes
- Faulty fuel system/fuel pump relay
- Open circuit or corrosion at fuse/relay socket or inline connector
- Short to ground on PCM relay control output or short to battery on supply feed
- Blown fuse protecting the relay coil or power feed
- PCM relay-driver failure (rare)
Fault status
Status
Open or short detected in fuel system relay control circuit — fuel pump relay control signal is out of expected range or continuity.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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