Code
P1274
GMC
P — Powertrain
Injectors Wired Incorrectly
AI status
Completed
Completed
100%
Causes
- Incorrect wiring after harness replacement or repair (pins swapped/miswired)
- Aftermarket or incorrect injector harness installed
- Damaged wiring harness or chafed insulation causing shorts or cross-connections
- Corroded or bent connector pins at injector or ECU/PCM
- Faulty or incorrectly installed electronic aftermarket parts (e.g., adapters, harness extensions)
- PCM/ECM connector damage or internal fault (less common)
Symptoms
- Check Engine Light (MIL) illuminated — P1274 stored
- One or more cylinder misfire or cylinder-specific misfire codes (P02xx)
- Rough idle or engine running rough under load
- Reduced power, hesitation, or poor throttle response
- Poor fuel economy and increased emissions
- No-start or hard-start if wiring causes injector failure on multiple cylinders
What to check
- Read and record freeze frame and all stored DTCs from the ECM
- Visually inspect injector harness, connectors, and ECM connector for damage, corrosion, or bent pins
- Confirm vehicle wiring diagram and injector pin assignments for cylinder numbering
- Check for aftermarket harnesses, adapters, or recent repairs at the intake or harness routing
- Measure injector resistance at each injector and compare to manufacturer spec
- Back-probe injector supply and driver terminals with key ON/crank to verify proper voltage and switching
Signal parameters
- Injector coil resistance: typical high-impedance injectors ~10–16 Ω, low-impedance/peak-and-hold ~2–4 Ω (check OEM spec)
- Connector supply voltage (pin common): battery voltage (~12 V) with key ON
- Injector driver signal: pulsed ground or pulsed positive from ECM (0–12 V swing) when cranking/running — pulse width varies with load/RPM
- No cross-continuity between injector signal circuits — open or short to other injector circuits should read OL or high continuity as appropriate
- Resistance/continuity from injector terminal to ECM pin: near 0 Ω to a few ohms (depending on harness length)
Diagnostic algorithm
- Retrieve codes and freeze-frame data; note which cylinder(s) may be affected and any associated misfire codes.
- Inspect visible wiring and connectors for damage, aftermarket adapters, or recent repair work. Verify injector connectors are seated and pins straight.
- Obtain OEM wiring diagram/pinout for the engine and identify injector-to-ECM pin assignments.
- With ignition OFF, disconnect injector connectors and measure each injector coil resistance; compare to spec to rule out internal injector faults.
- With connector still disconnected, check continuity from each injector terminal to the corresponding ECM pin. Verify correct mapping and that no two injector circuits are swapped.
- Check for shorts between injector signal circuits and to battery/ground. Repair any chafed wires or damaged insulation.
- With a back-probe or breakout harness and ignition ON/engine cranking, verify the common 12V supply at injectors and that the ECM provides the expected pulsed driver (use oscilloscope or multimeter to see switching).
- If a wiring fault is confirmed (swapped pins, short, open), repair by correcting pin positions, replacing damaged harness sections, or replacing connectors. Use proper crimping and OEM-style terminals.
- Clear codes and road-test. If code returns, compare injector drive waveforms with known-good reference or swap injectors (only if wiring confirmed correct) to isolate ECM vs injector driver faults.
- If wiring and injectors test normal and the mapping is correct, consider ECM/PCM inspection or reflash — consult manufacturer procedure before ECM replacement.
Likely causes
- Injector harness pins swapped at the ECM or injector connectors
- Harness repair used wrong pinout or connectors from a different engine variant
- Short between injector circuits in a damaged section of harness
- Connector corrosion or a bent terminal causing intermittent cross-feed
Fault status
Status
P1274 — Injectors Wired Incorrectly: ECM detects injector circuit mapping or signals that do not match expected configuration. Possible miswired harness, short/crossed circuit, or connector issue.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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