P1240

Code

CHEVROLET P — Powertrain

Injector Circuit Cylinder 7 Intermittent

Brand: CHEVROLET

Type: P — Powertrain

Views: UK: 29 EN: 68 RU: 36

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Page language: EN

Causes

Open, short, or intermittent wiring in injector circuit for cylinder 7
Corroded/loose connector at injector or PCM
Faulty fuel injector (coil or internal connection)
Poor power supply or ground to the injector circuit
Faulty PCM/driver transistor (less common)
Intermittent connector pin contact (water, corrosion, bent pin)

Symptoms

MIL (Check Engine) lamp illuminated intermittently
Occasional misfire or hesitation under load, often localized to cylinder 7
Rough idle or stumble that may come and go
Reduced fuel economy or loss of power during events when fault occurs
Fault stored intermittently; may not be present every key cycle

What to check

Read freeze frame and live data with a scan tool to capture conditions when fault set
Inspect injector connector for corrosion, bent pins, water intrusion or looseness
Backprobe injector connector to verify supply voltage and driver signal while cranking/running
Measure injector coil resistance and compare to OEM spec or to another known-good injector
Perform wiggle test on harness and connector with engine running to reproduce intermittent
Swap injector with another cylinder (if practical) and see whether code follows injector or stays with cylinder

Signal parameters

Injector supply terminal: steady battery voltage (~12–14 V) with ignition ON/running
Injector driver (PCM) toggles the injector circuit to ground (low-side) — look for pulsed waveform on driver side
Pulse width depends on load/RPM; at idle typical pulse widths are a few milliseconds and frequency equals injection events per cylinder
With oscilloscope: clean square/rectangular pulses between ~0 V (active) and near battery voltage (inactive) when the injector is being driven
Injector coil resistance: varies by model — compare with OEM spec or another cylinder; abnormal or highly variable resistance indicates a bad injector

Diagnostic algorithm

Connect a scan tool and record freeze-frame data and stored DTCs; note RPM, load, temperature when P1240 set.
Visually inspect the wiring harness and connector at cylinder 7 for damage, pin corrosion, or moisture.
With key ON (engine off) backprobe the injector connector: verify constant battery voltage on the supply terminal and check for good ground continuity on the ground side.
Start engine and monitor injector driver signal with a DVOM and/or oscilloscope. Look for pulsed grounding action and stable amplitude; watch for dropouts when fault occurs.
Measure injector coil resistance at the connector; compare to same-spec injector or factory spec. If values are erratic, suspect the injector.
Perform a swap test: move the cylinder 7 injector (and connector) to a known-good cylinder. Clear codes and run engine. If fault follows the injector, replace the injector; if it remains on cylinder 7, investigate wiring/PCM.
Perform a wiggle test on wiring and connectors while monitoring the injector signal to reproduce the intermittent fault.
Check continuity from the injector connector to the PCM pin with the harness disconnected. Check for short to ground or battery.
If wiring and injector check good, consult OEM wiring diagrams and test the PCM driver output; consider PCM replacement only after verifying external circuits are good.
Clear codes, road test and re-scan to confirm repair. If intermittent fault persists, document conditions and perform extended live-data monitoring or intermittent fault capture.

Likely causes

Damaged/chafed wiring or damaged connector at cylinder 7 injector
Corroded or loose injector connector causing intermittent contact
Failed injector (intermittent coil/open)
Intermittent PCM driver output for injector #7
Loose or corroded ground or fused power feed to the injector rail

Fault status

⚠️ Status

MIL ON — Injector Circuit Cylinder 7 Intermittent detected by PCM

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours

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P1240 — Injector Circuit Cylinder 7 Intermittent