Code
P0261
Generic
P — Powertrain
Cylinder 1 Injector A Circuit Low
AI status
Completed
Completed
100%
Causes
- Short to ground in injector harness (low resistance to ground)
- Damaged or shorted injector (internal short)
- Poor connection or corroded connector at injector
- Open or high-resistance supply (fuse, relay, power feed)
- Faulty PCM/ECU driver transistor or internal fault
- Low battery voltage or poor battery/charging system
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light
- Rough idle or misfire on cylinder 1
- Reduced power, hesitation or poor drivability
- Hard start or no-start (if injector not firing)
- Decreased fuel economy and increased emissions
What to check
- Read freeze frame and live data with a scan tool; note battery voltage and injector status
- Perform visual inspection of injector harness, connector, pins and protective sleeving
- Check battery and charging system voltage under load
- Measure injector coil resistance at the connector (with harness disconnected) and compare to spec
- Back-probe injector connector and observe voltage waveform with a scope or multimeter
- Check for short to ground or short to power in the wiring (ohm and voltage tests)
Signal parameters
- Resting (harness) supply voltage: approx. battery voltage (~11–14.5 V depending on system) with ignition ON
- Driver output when energized: low-side driver will pull circuit toward ground; observed voltage should drop near 0 V (pulsed)
- Typical solenoid injector cold resistance: commonly ~0.5–3.0 ohm (varies by design); piezo injectors have much higher resistance (check OEM spec)
- Injector current pulses: can range ~1–6 A during actuation (varies widely by type); use a clamp meter or current probe
- Pulse width: milliseconds range (depends on engine load/ECU strategy); verify waveform shape with oscilloscope
Diagnostic algorithm
- Safety first: allow engine to cool and isolate battery if doing wiring repairs. Use appropriate PPE.
- Clear DTCs, then start engine and verify P0261 returns. Note freeze-frame data (battery voltage, engine conditions).
- Visually inspect connector and wiring for damage, corrosion, pin deformation or signs of overheating at injector #1.
- With ignition OFF disconnect the injector harness and measure coil resistance across injector terminals; compare to OEM spec. If shorted (very low resistance) or open, replace injector.
- With connector disconnected and ignition ON, measure supply voltage at the injector harness power terminal — should be battery voltage. If low or missing, trace power feed, fuses and relays.
- Back-probe the driver terminal while cranking/running and observe waveform with a DVOM (frequency/pulse) or oscilloscope. Confirm pulses and that voltage is pulled toward ground when energized. No pulsing or constant low indicates short to ground or driver fault.
- Measure resistance from driver pin to chassis ground to check for short to ground in wiring (with harness connected and ignition OFF).
- Perform a wiggle test on wiring while monitoring live data or scope for intermittent changes. Repair chafing or broken wires.
- Swap injector #1 with another identical cylinder. If the code follows the injector, replace the injector. If code stays on cylinder 1, suspect wiring or PCM.
- If wiring checks good and injector is good, test PCM driver output for correct switching and load-handling. If driver fails, replace PCM per OEM procedure.
- After repairs, clear codes and perform a road or dyno test to confirm repair and that DTC does not return.
Likely causes
- Damaged or shorted wiring between injector #1 and ECM (most common)
- Corroded/bent pins or poor connector contact at the injector
- Failed injector (coil shorted)
- PCM driver failure (less common)
- Low system voltage or blown/loose fuse/relay
Fault status
Status
P0261 — Cylinder 1 Injector A Circuit Low: The ECM/PCM detected a lower-than-expected voltage/current on the injector A driver for cylinder 1, indicating a short to ground, faulty injector, wiring or driver defect. Service wiring, connectors, injector and control module as required.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Repair manuals
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Code
P0261
GWM
P — Powertrain
- Low Cylinder Injector Circuit Value 1
AI status
Completed
Completed
100%
Causes
- Short to ground in injector harness (low resistance to ground)
- Damaged or shorted injector (internal short)
- Poor connection or corroded connector at injector
- Open or high-resistance supply (fuse, relay, power feed)
- Faulty PCM/ECU driver transistor or internal fault
- Low battery voltage or poor battery/charging system
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light
- Rough idle or misfire on cylinder 1
- Reduced power, hesitation or poor drivability
- Hard start or no-start (if injector not firing)
- Decreased fuel economy and increased emissions
What to check
- Read freeze frame and live data with a scan tool; note battery voltage and injector status
- Perform visual inspection of injector harness, connector, pins and protective sleeving
- Check battery and charging system voltage under load
- Measure injector coil resistance at the connector (with harness disconnected) and compare to spec
- Back-probe injector connector and observe voltage waveform with a scope or multimeter
- Check for short to ground or short to power in the wiring (ohm and voltage tests)
Signal parameters
- Resting (harness) supply voltage: approx. battery voltage (~11–14.5 V depending on system) with ignition ON
- Driver output when energized: low-side driver will pull circuit toward ground; observed voltage should drop near 0 V (pulsed)
- Typical solenoid injector cold resistance: commonly ~0.5–3.0 ohm (varies by design); piezo injectors have much higher resistance (check OEM spec)
- Injector current pulses: can range ~1–6 A during actuation (varies widely by type); use a clamp meter or current probe
- Pulse width: milliseconds range (depends on engine load/ECU strategy); verify waveform shape with oscilloscope
Diagnostic algorithm
- Safety first: allow engine to cool and isolate battery if doing wiring repairs. Use appropriate PPE.
- Clear DTCs, then start engine and verify P0261 returns. Note freeze-frame data (battery voltage, engine conditions).
- Visually inspect connector and wiring for damage, corrosion, pin deformation or signs of overheating at injector #1.
- With ignition OFF disconnect the injector harness and measure coil resistance across injector terminals; compare to OEM spec. If shorted (very low resistance) or open, replace injector.
- With connector disconnected and ignition ON, measure supply voltage at the injector harness power terminal — should be battery voltage. If low or missing, trace power feed, fuses and relays.
- Back-probe the driver terminal while cranking/running and observe waveform with a DVOM (frequency/pulse) or oscilloscope. Confirm pulses and that voltage is pulled toward ground when energized. No pulsing or constant low indicates short to ground or driver fault.
- Measure resistance from driver pin to chassis ground to check for short to ground in wiring (with harness connected and ignition OFF).
- Perform a wiggle test on wiring while monitoring live data or scope for intermittent changes. Repair chafing or broken wires.
- Swap injector #1 with another identical cylinder. If the code follows the injector, replace the injector. If code stays on cylinder 1, suspect wiring or PCM.
- If wiring checks good and injector is good, test PCM driver output for correct switching and load-handling. If driver fails, replace PCM per OEM procedure.
- After repairs, clear codes and perform a road or dyno test to confirm repair and that DTC does not return.
Likely causes
- Damaged or shorted wiring between injector #1 and ECM (most common)
- Corroded/bent pins or poor connector contact at the injector
- Failed injector (coil shorted)
- PCM driver failure (less common)
- Low system voltage or blown/loose fuse/relay
Fault status
Status
P0261 — Cylinder 1 Injector A Circuit Low: The ECM/PCM detected a lower-than-expected voltage/current on the injector A driver for cylinder 1, indicating a short to ground, faulty injector, wiring or driver defect. Service wiring, connectors, injector and control module as required.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
P0261
HUMMER
P — Powertrain
Cylinder 1 Injector Circuit Low
AI status
Completed
Completed
100%
Causes
- Short to ground in injector harness (low resistance to ground)
- Damaged or shorted injector (internal short)
- Poor connection or corroded connector at injector
- Open or high-resistance supply (fuse, relay, power feed)
- Faulty PCM/ECU driver transistor or internal fault
- Low battery voltage or poor battery/charging system
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light
- Rough idle or misfire on cylinder 1
- Reduced power, hesitation or poor drivability
- Hard start or no-start (if injector not firing)
- Decreased fuel economy and increased emissions
What to check
- Read freeze frame and live data with a scan tool; note battery voltage and injector status
- Perform visual inspection of injector harness, connector, pins and protective sleeving
- Check battery and charging system voltage under load
- Measure injector coil resistance at the connector (with harness disconnected) and compare to spec
- Back-probe injector connector and observe voltage waveform with a scope or multimeter
- Check for short to ground or short to power in the wiring (ohm and voltage tests)
Signal parameters
- Resting (harness) supply voltage: approx. battery voltage (~11–14.5 V depending on system) with ignition ON
- Driver output when energized: low-side driver will pull circuit toward ground; observed voltage should drop near 0 V (pulsed)
- Typical solenoid injector cold resistance: commonly ~0.5–3.0 ohm (varies by design); piezo injectors have much higher resistance (check OEM spec)
- Injector current pulses: can range ~1–6 A during actuation (varies widely by type); use a clamp meter or current probe
- Pulse width: milliseconds range (depends on engine load/ECU strategy); verify waveform shape with oscilloscope
Diagnostic algorithm
- Safety first: allow engine to cool and isolate battery if doing wiring repairs. Use appropriate PPE.
- Clear DTCs, then start engine and verify P0261 returns. Note freeze-frame data (battery voltage, engine conditions).
- Visually inspect connector and wiring for damage, corrosion, pin deformation or signs of overheating at injector #1.
- With ignition OFF disconnect the injector harness and measure coil resistance across injector terminals; compare to OEM spec. If shorted (very low resistance) or open, replace injector.
- With connector disconnected and ignition ON, measure supply voltage at the injector harness power terminal — should be battery voltage. If low or missing, trace power feed, fuses and relays.
- Back-probe the driver terminal while cranking/running and observe waveform with a DVOM (frequency/pulse) or oscilloscope. Confirm pulses and that voltage is pulled toward ground when energized. No pulsing or constant low indicates short to ground or driver fault.
- Measure resistance from driver pin to chassis ground to check for short to ground in wiring (with harness connected and ignition OFF).
- Perform a wiggle test on wiring while monitoring live data or scope for intermittent changes. Repair chafing or broken wires.
- Swap injector #1 with another identical cylinder. If the code follows the injector, replace the injector. If code stays on cylinder 1, suspect wiring or PCM.
- If wiring checks good and injector is good, test PCM driver output for correct switching and load-handling. If driver fails, replace PCM per OEM procedure.
- After repairs, clear codes and perform a road or dyno test to confirm repair and that DTC does not return.
Likely causes
- Damaged or shorted wiring between injector #1 and ECM (most common)
- Corroded/bent pins or poor connector contact at the injector
- Failed injector (coil shorted)
- PCM driver failure (less common)
- Low system voltage or blown/loose fuse/relay
Fault status
Status
P0261 — Cylinder 1 Injector A Circuit Low: The ECM/PCM detected a lower-than-expected voltage/current on the injector A driver for cylinder 1, indicating a short to ground, faulty injector, wiring or driver defect. Service wiring, connectors, injector and control module as required.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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.
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