Comprehensive diagnostic guide for OBD-II code P2155

Code reference

• P2155 generally corresponds to an injector group fault in the fuel injector circuit supply. Specifically, the Open Source code definition lists it as: Source: Open Source definition
• Context: In OBD-II, P-codes are Powertrain codes. P2155 is categorized under Powertrain Codes, and OBD-II diagnostics cover fuel/injection, engine management, and related systems. Source: OBD-II > Diagnostic Trouble Codes and > Powertrain Codes
• Emissions impact: A MIL/CEL may illuminate with P2155 and can lead to an emissions test failure if unresolved. Source: Wikipedia Emissions Testing

What This Code Means

• The engine's PCM/ECU is detecting an open/open-circuit condition in the supply side for Fuel Injector Group D. In practical terms, the PCM is not getting a proper power-supply signal to energize the injectors in group D, which can cause misfires or fuel delivery issues for the cylinders served by that injector group.

Symptoms

• MIL/Check Engine Light on with P2155 stored (may be accompanied by P030x misfire codes if misfires occur)
• Rough idle or rough engine running, particularly when the engine is at idle or under light load
• Hesitation or stumble during acceleration when demand shifts to group D injectors
• Degraded fuel economy or odd fuel trims when data is reviewed with a scan tool
• Occasional engine performance drop-offs during cold starts or during mild torque requests
  Note: These symptom patterns are consistent with a loss of injector group D power delivery, as would be indicated by P2155.

Probable Causes

• injector group D power supply circuit open or high resistance in wiring/connector to the PCM or injector harness (most common)
• faulty injector group D injector(s) or group D injector driver (PWM/PI signaling) in the PCM
• blown fuse, fusible link, or relay controlling injector group D power supply
• wiring harness abrasion, corrosion, or poor connector seating in the injector supply path
• PCM/ECU fault or software issue affecting the injector drive channel
• intermittent ground issue affecting the injector return path (less common for a "supply circuit/open" fault but possible if a shared ground path is involved)

Cause Probability

• Wiring/connectors and open-circuit in injector supply to group D: ~40-60%
• Injector(s) or driver (PCM channel) fault: ~20-30%
• Fuse/relay or power supply fault (including voltage drop scenarios): ~5-15%
• PCM/ECU fault or software issue: ~5-10%
• Ground/connector integrity issues in the group D circuit: ~5-10%
  Note: These figures reflect typical field experience; exact distribution varies by vehicle make/model and maintenance history. If you have access to local NHTSA complaint data, that would tailor these numbers further; otherwise use your diagnostic results and symptoms to guide the emphasis.

What to gather and what tools you'll need

• Personal safety: disconnect the battery before significant harness work; ensure you're protected against accidental short circuits; follow shop safety procedures
• Scan tool capable of reading live data andFreeze-Frame data
• Multimeter (DC voltage/continuity testing)
• Wire-probe or breakout lead kit for injector harness testing
• Injector resistance tester or ohmmeter (comparator against manufacturer spec)
• Optional: oscilloscope to view injector duty cycle and pulse timing
• Vehicle service information for exact injector group mapping and wiring diagrams (manufacturer-specific; the P2155 definition implies Group D, but mapping varies by model)

Diagnostic Approach

1) Confirm and contextualize

• Read DTC with the engine off and with the engine running (live data). Note any accompanying codes (e.g., P030x misfires, P017x fuel trim, P035x injector-related codes).
• Check Freeze Frame data to understand operating conditions when P2155 was captured (engine temperature, RPM, load, fuel trims).

2) Visual and basic electrical inspection

• Inspect the injector group D power supply circuit harness and its connector for signs of damage, corrosion, moisture, or looseness.
• Inspect the fuse/relay and the wiring path from the battery/PNC supply to the injector group D connector; look for pin corrosion or chafed insulation.
• Confirm the ground path for injector group D return is intact where applicable (some diagrams show shared grounds or reference grounds for injector drivers).

3) Verify presence of power and reference signals

• With key on (engine off) test for battery voltage on the injector group D feed circuit at the injector connector or at the PCM harness side. If there is no voltage, the issue is upstream (fuse/relay, wiring, or PCM control circuit).
• With the engine cranking or running, verify that the injector group D supply voltage is present and stable. A lack of supply or repeated voltage dips can indicate an open circuit, poor connection, or a failing supply circuit.
• Check for a proper ground on the injector group D circuit and/or injector return path as specified by the vehicle's wiring diagram.

4) Determine injector resistance and driver integrity

• Measure the resistance of the injector coils in Group D. Compare to manufacturer specification. A faulty injector coil can load the circuit or distort readings, but an open/short is more characteristic of a supply problem if the supply path checks out.
• If possible, test the injector driver path (the PCM output) by using a known-good injector to see if the injector group D channel energizes or by performing a controlled load test with a current/voltage measurement at the PCM side.

5) Check for voltage drop and continuity

• Perform a voltage drop test across fuses, fusible links, and connectors in the Group D power supply path while the PCM is attempting to energize the injectors. Any abnormal drop indicates resistance in harness or a loose connection.

6) Isolate and verify

• If you have a known-good injector or a spare harness segment, swap or back-probe to determine if the issue follows the injector group or remains with the wiring/PCM.
• If all wiring and supply checks pass but the problem persists, consider PCM/driver failure as a possibility (less common but plausible).

7) Test results interpretation

• If 12V (or specified supply voltage) is present at the Group D feed with key on and no injector activation, suspect an open circuit, broken conductors, or PCM shutdown of the channel.
• If voltage is present but current draw is zero or erratic, suspect an open in the injector or an internal PCM fault in the Group D channel.
• If voltage and current appear normal but misfire codes persist, re-check mechanical contributions (air leaks, vacuum leaks near the intake), fuel pressure, or other related sensor data that can influence fuel delivery perception.

8) Post-repair verification

• Clear codes and run a drive cycle to re-check for P2155. Verify absence of P2155 and absence of new injector-related codes.
• Confirm no related P030x codes reappear and monitor fuel trim data to ensure stability.
• Confirm proper engine performance through acceleration tests and idle stability.

What to do about possible root causes (repair actions)

• If an open circuit or damaged wiring/connector is found in the Group D supply path: repair or replace the wiring harness; repair or replace the connector; ensure secure mating and proper locking.
• If a fuse/relay/fusible link is found defective: replace with correct rating and verify circuit operation.
• If an injector group D injector or its driver is suspected: replace the injector or perform a PCM injector-driver channel diagnostic; if the driver is at fault, PCM replacement or reprogramming may be necessary (verify with the vehicle manufacturer's service information and any ready-to-run test procedures).
• If the PCM/ECU channel is determined to be faulty and no harness faults exist: PCM replacement or reprogramming per OEM guidance may be required.
• After any repair, re-check all related circuits and confirm that P2155 does not reappear.

Important Notes

• OBD-II uses standardized diagnostic trouble codes (DTCs), with P-codes designated for powertrain-related issues, including injector circuits. This standardization is described in the OBD-II overview (Diagnostic Trouble Codes and Powertrain Codes). Source: Wikipedia
• Emissions testing guidance indicates that failure to clear or properly diagnose P-codes like P2155 can affect emissions testing and MIL status. Source: Wikipedia Emissions Testing

Safety Considerations

• Disconnect the battery before performing mechanical or electrical work that could short or energize circuits.
• Use proper PPE when working around fuel systems, and avoid sparks near the fuel rail or injectors.
• When diagnosing electrical circuits, use proper insulation and test equipment to prevent accidental shorts and to avoid misinterpreting transient readings as failures.
• If you're unsure about the injector group mapping for a specific vehicle, consult the OEM wiring diagram to locate Group D injectors, as group labeling varies by manufacturer and engine/valve train configuration.

Summary

• P2155 indicates an open circuit or supply issue for Fuel Injector Group D. The most common causes involve wiring/connectors, fuses/relays, and the injector driver path. A systematic approach-verify power and ground, inspect wiring and connectors, measure injector resistance, and test the PCM driver path-helps identify whether the fault is a harness issue, injector, PCM channel, or a combination. After repairs, clear codes, and perform a drive cycle to confirm the issue is resolved and emissions readiness is restored.

• Open Source code definition for P2155: (description of the code meaning)

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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