Code
P1237
SATURN
P — Powertrain
Injector Circuit Cylinder 6 Intermittent
Views:
UK: 20
EN: 33
RU: 28
AI status
Completed
Completed
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Causes
- Intermittent/open/short in injector wiring harness to cylinder 6
- Corroded/loose injector connector or terminal
- Faulty fuel injector (intermittent internal failure)
- Poor power or ground supply to injector rail or ECM
- Intermittent PCM/ECM driver fault or poor ECM connector contact
- Water/contamination in connector or wiring harness damage from heat/chafe
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated (engine light)
- Intermittent misfire on cylinder 6 (may show as P0306 alongside P1237)
- Rough idle or rough running under load
- Hesitation, reduced engine power or poor fuel economy
- Occasional stalling or stumble that comes and goes
What to check
- Read freeze frame and all stored/pending codes; note if P0306 or other injector codes present
- Visually inspect wiring and connector for cylinder 6 for corrosion, bent pins, damage, or water intrusion
- Perform wiggle/drive test while monitoring live data to reproduce intermittent condition
- Measure injector coil resistance at connector (key off) and compare to specification
- Backprobe injector connector while cranking/idle to observe driver pulses and supply voltage
- Check continuity between injector connector pins and ECM connector pins; check ECM grounds and main power supply to injector rail
Signal parameters
- Key ON (engine off): at injector + supply (battery feed) ≈ battery voltage (~12 V)
- Injector coil resistance (typical low-impedance injectors) commonly ~10–18 ohms — refer to factory spec for exact value
- Driver signal: pulsed ground or switched low/high depending on system; expected pulse waveform (clean rectangular pulses) when engine cranks or runs
- Pulse width varies with load; idle pulses commonly 1–5 ms, increases with load; frequency matches engine RPM (pulses per injection event)
- Intermittent fault may show intermittent loss of pulses, shorted pulse (stuck high/low), or noisy/distorted waveform on oscilloscope
Diagnostic algorithm
- Retrieve codes and freeze frame data; note operating conditions when fault set. 2) Perform visual inspection of injector #6 harness and connector for damage, corrosion, water, or loose pins. 3) Check for related misfire codes (P0306) and monitor cylinder 6 trim/live misfire counters. 4) With key off, measure injector #6 coil resistance and compare to spec. 5) With key on and engine cranking/running, backprobe injector connector: verify constant battery feed at supply pin and pulsed driver at control pin. 6) Wiggle the harness/connector while monitoring pulses to try to reproduce intermittent condition. 7) Check continuity from injector connector to ECM connector and check ECM ground(s) and power feed for proper voltage and integrity. 8) If intermittent continues and wiring/connector check good, swap injector #6 with another cylinder to see if code follows the injector. 9) If code follows injector, replace injector; if code remains on cylinder 6, inspect/repair wiring or connector; if wiring/connector OK, suspect ECM driver — confirm with manufacturer procedure before ECM replacement. 10) Clear codes and test drive to verify repair. Record results and retest if intermittent condition recurs.
Likely causes
- Damaged insulation or chafed wire causing intermittent short to ground or to battery
- Corroded terminal at injector connector producing intermittent contact
- Internal injector coil failure that changes resistance under vibration/heating
- Faulty ECM injector driver or poor ECM pin contact
- Weak or intermittent battery/ignition voltage to injector supply circuit
Fault status
Status
P1237 — Injector Circuit Cylinder 6 Intermittent: ECM detected an intermittent fault (open/short or loss of command) in the fuel injector circuit for cylinder #6.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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