Code
P1243
HUMMER
P — Powertrain
Injector Circuit Cylinder 8 Intermittent
AI status
Completed
Completed
100%
Causes
- Damaged or chafed injector wiring harness to cylinder 8
- Poor or corroded connector at the injector (pins or sockets)
- Faulty fuel injector (coil open/intermittent) for cylinder 8
- Loose or poor low-side driver (ground) or high-side supply at the injector
- Intermittent short to battery or ground from movement/vibration
- Poor ground or battery supply to the engine control module (ECM) or injector rail
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated intermittently
- Intermittent or consistent misfire on cylinder 8 (may be occasional)
- Rough idle or engine hesitation under load
- Reduced fuel economy or reduced engine power
- Diagnostic trouble codes for injector circuit or cylinder misfire present (may be intermittent)
What to check
- Retrieve freeze-frame and scan tool data — note conditions when code set (RPM, temp, load)
- Visually inspect wiring and connector for cylinder 8 for damage, corrosion, bent pins, or poor seating
- Perform wiggle test of harness/connectors while observing live data or watching DTCs
- Check injector connector pins for voltage (key on) and continuity to ECM (refer to wiring diagram)
- Measure injector coil resistance at the connector (with harness disconnected) and compare to specification
- Backprobe injector connector while cranking/running to verify pulsed driver and steady battery feed
Signal parameters
- Injector coil resistance (typical): low-impedance ~1–3 Ω or high-impedance ~10–16 Ω depending on injector design — check OEM spec
- Battery/supply voltage at injector high-side: ~11–14 V with ignition on
- Injector driver is low-side switching to ground; when energized expect a pulsed waveform on the driver pin (0 V during ON if switching to ground)
- Pulse width varies by load and RPM — commonly 1–10 ms during normal operation; frequency increases with RPM
- When idle/not-firing, driver should not be continuously grounded (no constant ON)
Diagnostic algorithm
- Read and record DTCs and freeze-frame data with a scan tool. Note conditions when P1243 occurred (engine temp, rpm, load).
- Perform visual inspection of cylinder 8 injector harness and connector for damage, corrosion, or loose pins. Repair any visible issues.
- Clear codes and perform a wiggle test of harness/connectors while monitoring live data or DTC status to reproduce the intermittent fault.
- Measure injector coil resistance (with harness disconnected). Compare to manufacturer spec. If out of range or intermittent, replace injector.
- Backprobe high-side supply pin at injector with ignition ON to confirm battery voltage present. Check continuity to fuse/rail if absent.
- Backprobe low-side driver pin while cranking/running. Use a noid light or oscilloscope to verify pulsed signal. If no pulse, trace driver circuit to ECM.
- Check continuity between injector connector and ECM pin for opens/shorts to ground or battery. Wiggle harness and re-check continuity to locate intermittent wiring faults.
- Swap the suspect injector with another known-good injector of same type (if practical) and re-scan. If code follows injector, replace injector. If code remains on cylinder 8, suspect wiring/ECM.
- Inspect and test engine ground and ECM power/ground circuits. Repair poor grounds and retest.
- If wiring and injector check good and intermittent persists, consult OEM tech service bulletins and consider ECM driver testing or replacement as last resort.
- After repairs, clear codes and perform a road/test drive under conditions that previously set the code to confirm repair.
Likely causes
- Loose/dirty/corroded injector connector at cylinder 8
- Broken or intermittently shorted wire in the harness (pinch, rubbing, or flex point)
- Faulty injector coil (intermittent internal break)
- Poor ground or power feed for the injector circuit
- ECM output driver intermittently failing (less common)
Fault status
Status
P1243 — Injector Circuit Cylinder 8 Intermittent: PCM detected an intermittent fault in the injector circuit for cylinder 8. Check wiring, connector, injector, and ECM driver.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
Browse 138 HUMMER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.
HUMMER
-
HUMMER: 2009
-
HUMMER: 2008
-
HUMMER: 2007
-
HUMMER: 2005
-
HUMMER: 2004
-
HUMMER: 2000
-
HUMMER: 1999
-
HUMMER: 1994
-
HUMMER: 1993
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email