Code
P1225
GMC
P — Powertrain
Injector Circuit Cylinder 2 Intermittent
Views:
UK: 28
EN: 45
RU: 33
AI status
Completed
Completed
100%
Causes
- Broken, chafed, corroded or loose wiring/connector at injector 2
- Poor connector pin contact or bent terminal
- Failed or intermittent fuel injector (internal short/open)
- Short to battery or ground in injector harness
- Faulty power/ground supply to injector rail or ECM
- Intermittent or damaged injector driver output in the PCM/ECM
Symptoms
- Check Engine Light (CEL) may be steady or flashing when misfire occurs
- Intermittent rough idle or hesitation under load
- Occasional misfire on cylinder 2 (possible engine stumble)
- Reduced fuel economy or poor drivability
- Diagnostic trouble code P1225 stored (intermittent)
What to check
- Read DTCs and freeze frame/pending codes with a scan tool; note when fault occurred
- Visually inspect injector 2 connector, pins and wiring for corrosion, damage or loose terminals
- Wiggle harness and connector while monitoring live data or misfire counters to reproduce the fault
- Check injector resistance with an ohmmeter and compare to specification
- Back-probe injector connector with a noid light or oscilloscope to confirm pulse and voltage
- Check battery voltage at the injector connector with key on and during cranking
Signal parameters
- Supply voltage at injector connector (key ON): ~11–14 V (battery voltage)
- Injector coil resistance: commonly ~10–16 Ω for high-impedance injectors or ~2–4 Ω for low-impedance types (check vehicle spec)
- Injector pulse width at idle: approx 1–5 ms (varies with load and engine speed)
- Injector drive: PCM switches the injector to ground; resting side is held at battery voltage
- Oscilloscope waveform: steady battery voltage when OFF, regular ground pulses when ON; look for missing pulses or abnormal voltage spikes/transients
Diagnostic algorithm
- Verify code and data: connect a scan tool and confirm P1225 is current or intermittent; record freeze frame and misfire counts.
- Visual inspection: check connector, pins, wiring harness routing for chafe, heat damage, corrosion, or recent repair areas.
- Wiggle test: with a helper or using live data, gently manipulate the injector connector/harness while monitoring injector pulse, misfire counts, or CEL to reproduce the intermittent condition.
- Measure resistance: disconnect injector and measure coil resistance; compare to spec. Large deviation suggests a bad injector.
- Power/ground check: with connector disconnected, check for battery voltage on the supply terminal and good ground switching on the driver terminal when cranking (use a noid light or voltmeter/back-probe carefully).
- Pulse verification: use a noid light or oscilloscope on the injector driver lead while cranking or running to confirm consistent pulses and waveform integrity. Watch for missing pulses, intermittent loss, or abnormal spikes.
- Swap test: swap injector 2 with another cylinder's injector (and swap connectors if needed). If the problem follows the injector, replace the injector; if it stays with cylinder 2, suspect wiring/PCM.
- Wiring continuity: if swapping did not isolate, test continuity and resistance from injector connector to PCM driver pin; look for intermittent opens or high resistance.
- Inspect PCM: check PCM connector pins for corrosion, bent pins, or water ingress. Verify PCM power and grounds are stable. If all harness and injector checks are good, consider PCM driver failure and consult manufacturer guidance before replacement.
- Repair and verify: repair wiring or replace faulty injector/connector/PCM as indicated. Clear codes and perform test drive to ensure the intermittent condition is resolved and no new codes appear.
Likely causes
- Corroded or loose connector at cylinder 2 injector
- Damaged harness (chafed wire, broken strand) between injector and ECM
- Faulty injector 2 with intermittent internal connection
- Bad PCM/ECM driver (less common) or poor PCM ground/power
Fault status
Status
Intermittent fault detected in fuel injector circuit for cylinder 2. Electrical connection or driver output is intermittent (open, short, or poor contact). Monitor and test wiring, connector and injector.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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