Comprehensive diagnostic guide for OBD-II code P1357

Note: P1357 is not a universally standardized OBD-II generic code. The provided open-source reference describes it as "Ignition monitor de diagnóstico pulsewidth não definido" (Ignition monitor diagnostic pulse width not defined), which suggests this may be a manufacturer-specific or OEM-specific code in some systems. Wikipedia's OBD-II sections confirm that OBD-II uses diagnostic trouble codes (DTCs) to monitor powertrain parameters and can include manufacturer-specific codes. Given the sources, treat P1357 as potentially OEM-specific and use OEM diagnostics when available.

1) What the code means (definition and scope)

• Primary meaning from the open-source reference: Ignition monitor diagnostic pulse width not defined. This implies the ignition monitor (engine ignition/control system) did not provide a defined/predictable pulse width signal that the PCM/engine controller expects.
• Important caveat: P1357 is not a universal standard code; its exact meaning, test procedure, and corrective action can vary by vehicle make/model. Always cross-check with the vehicle's OEM service information, TSBs, and the relevant factory diagnostic procedure.

2) Likely symptoms you may observe

• Malfunction indicator lamp (MIL) or check engine light ON.
• Intermittent or consistent rough idle, misfires on one or more cylinders.
• Reduced engine power, hesitation, or stumbling under acceleration.
• Poor fuel economy or abnormal engine performance.
• In some cases, no obvious symptoms aside from the MIL while the vehicle drives normally otherwise.
  Note: These symptom descriptions reflect common user complaints seen with ignition/monitoring DTCs in OBD-II contexts and typical powertrain code presentation.

3) Quick diagnostic plan (high-level flow)

• Verify the code and status:
  • Confirm P1357 is present with a current DTC; note any freeze-frame data and related codes.
  • Check readiness monitors and whether any other codes accompany P1357 (misfire, ignition coil, sensor, or PCM faults often co-occur).
• Gather baseline data:
  • Scan for live data: ignition coil signals, primary current or PWM duty cycle, cylinder misfire counters, battery voltage, and sensor inputs (CMP/CKP, CKP, or other crank/ cam sensors as applicable).
  • Look for abnormal PWM or pulse width signals, or "not defined"/invalid readings in live data.
• Perform a targeted physical inspection:
  • Inspect ignition system components (coil packs, spark plugs, secondary spark plug wires) and ignition coil connectors for damage, corrosion, or overheating.
  • Inspect wiring harnesses and connectors to the ignition coils, PCM, and ignition control module for damage, loose connections, or corrosion.
  • Inspect the crankshaft and camshaft position sensor wiring and connectors; verify timing if applicable.
  • Check battery health and charging voltage; ensure stable power supply to the ignition and ECU circuits.
• If needed, perform diagnostic tests specific to ignition system and monitoring:
  • Coil pack swap test (where applicable) to determine if the fault follows a coil versus a cylinder, indicating a coil or wiring issue.
  • Measure ignition coil primary resistance and, if possible, secondary resistance against OEM specs.
  • Use an oscilloscope or a high-quality scan tool to view ignition waveform, dwell time, and PWM signals; look for meaningless or undefined pulse width data.
  • Check for OEM service bulletins or software updates that address ignition monitor timing/pulse width monitoring.
• OEM and software considerations:
  • If the problem seems software/monitoring related, verify PCM/ECU software version, any published fixes, and whether a reflash or calibration update is available.
  • Some OEMs may require a dealership-level diagnostic procedure to clear/defeat the monitor or reinitialize the ignition timing logic after a fix.

4) Step-by-step diagnostic procedure (practical, actionable)

Data collection and initial verification

• Use a capable OBD-II scanner to confirm P1357 and pull freeze-frame data.
• Note any accompanying codes (e.g., misfire codes P030x, ignition coil related codes, crank/cam sensor codes, or PCM fault codes).
• Check live data:
  • Battery voltage (should be ~12.6 V engine OFF; ~13.5-14.5 V with engine RUNNING).
  • Ignition coil primary voltage/current/dwell or PWM signal for each cylinder/coil.
  • Secondary ignition data (spark plug voltage or energy, if your tool provides it).
  • Crankshaft/camshaft sensor readings (CKP/CMP) and reference signals.
• If the tool can show a "pulse width" or PWM parameter, note whether it is defined, normal, or undefined.

Visual and basic electrical checks

• Inspect ignition coils and pack(s) for signs of overheating, cracks, arcing, or oil contamination.
• Inspect spark plugs for wear or fouling; replace if worn beyond spec.
• Inspect wiring harnesses and connectors to ignition coils, PCM, and ignition drivers for corrosion, bent pins, or damaged insulation.
• Check ignition coil connector seals and grounds; ensure a solid ground path from coil to engine/PCM.
• Inspect battery and charging system; ensure grounds from engine block to vehicle chassis are clean and tight.

Targeted electrical tests (where safe and appropriate)

• Coil pack tests:
  • Measure coil primary resistance and compare to OEM specifications.
  • Swap coils between cylinders (if the code seems related to a particular coil) and see if P1357 moves with the coil, which would indicate a coil or pack issue.
• Signal integrity tests (advanced):
  • Use an oscilloscope to view primary coil current waveform and dwell time; look for abnormal duty cycles, irregular waveforms, or undefined pulse widths.
  • Check CKP/CMP sensor signals for clean, consistent edges and correct timing references; replace sensors if erratic.
• Wiring verification:
  • Check for continuity and short-to-ground/short-to-Vin conditions in ignition coil control circuits and PCM driver circuits.
  • Check for opens or high resistance in the circuit between the PCM/ignition driver and ignition coils.
• PCM/ECU considerations:
  • Confirm there are no PCM faults, memory corruption, or software issues. Consider OEM dealer-level diagnostics or reflash if indicated by OEM service information.
  • Look for TSBs addressing ignition monitor/pulse width or similar monitor-related DTCs; apply recommended procedure if available.

Optional cross-checks and follow-up

• Clear the codes and drive the vehicle under controlled conditions to see if the code reappears and if any symptoms return.
• If P1357 reappears and tests point away from ignition hardware, re-evaluate sensors (CKP/CMP), timing, and power/ground integrity.
• If the code seems to be purely a monitor-definition issue (not a measurable hardware fault), verify OEM diagnostic steps to re-initialize or reprogram the ignition monitor within the ECU.

5) Probable causes and approximate likelihood (ASE-field experience guidance)

Because the exact OEM interpretation of P1357 can vary, provide the following generalized likelihoods for ignition-monitor/pulse-width related issues. These are approximate ranges and depend heavily on vehicle make/model, prior maintenance, and whether the issue is hardware or software in nature:

• Faulty ignition coil(s) or coil pack/driver circuit (primary/secondary winding, PWM drive): 30-40%
• Wiring/connector problems to ignition coils, coil drivers, or ECU (corrosion, damaged insulation, loose pins): 20-35%
• PCM/ECU or ignition control module fault or software/firmware issue: 15-25%
• Sensor issues in the ignition/ timing path (CKP/CMP) or related timing references: 10-15%
• Battery/charging system or general power supply issues causing unstable monitor signals: 5-10%
• Other/unknown factory-specific causes (e.g., monitor initialization issue, TSB-required fixes): up to ~5%

Notes:

• These percentages reflect typical field observations for ignition-monitor-type DTCs in modern vehicles and are not vendor-specific. The distribution can shift depending on whether the fault is mechanical (coils, wiring), electrical (diagnostic wiring, grounds), sensor timing, or software/ECU related.
• Since P1357 is not a universal standard code, engine-specific mappings may differ. Always refer to OEM diagnostic procedures and dealer service information when available.

6) Safety considerations

• High-voltage ignition system: risk of electric shock and arc. Do not probe live coils directly with a bare metal tool; maintain appropriate PPE and de-energize the system when performing disconnections.
• Always disconnect the battery before performing electrical wiring work on ignition circuits; follow proper lockout/tagout procedures where applicable.
• Use insulated tools and follow vehicle service manual procedures for coil pack removal to avoid short circuits or damage to connectors.
• When using an oscilloscope or power supplies for testing, ensure the vehicle is securely supported and away from moving parts.

7) Documentation and data to capture

• DTC list and freeze-frame data (time, engine load, RPM, temp, fuel trim if available).
• Readouts for ignition coil primary voltage/current or PWM duty cycle per coil.
• CKP/CMP sensor waveforms or digital readings if available.
• Battery voltage and charging conditions during testing.
• OEM-reported test steps or TSB references if applicable.

8) Common fixes (priorities)

• Replace faulty ignition coil(s) or coil pack and repair/replace damaged coil wiring or connectors.
• Repair or replace damaged harnesses or connectors to ignition coils, PCM, or related drivers; apply proper shields/grounding as needed.
• Replace or recalibrate CKP/CMP sensors if they are defective or providing erratic signals.
• Verify and/or reflash or update PCM/ECU software as per OEM guidelines; apply any applicable TSBs.
• Repair or replace failing grounds and ensure solid chassis/engine ground connections.
• If software/monitor initialization is the root cause, follow OEM procedures to reinitialize the ignition monitor or ECU, as appropriate.

9) References (for quick lookup)

• Wikipedia - OBD-II: Diagnostic Trouble Codes: general description of how DTCs are used in modern OBD-II systems to monitor parameters and trigger MILs.
• Wikipedia - OBD-II: Powertrain Codes: overview of powertrain-related DTCs within OBD-II.
• Wikipedia - OBD-II: Emissions Testing: context of how DTCs relate to emissions and regulatory testing.
• Open Source - Code definition: Ignition monitor de diagnóstico pulsewidth não definido (Ignition monitor diagnostic pulse width not defined). This is the key non-standard interpretation that P1357 may reflect in some contexts.

Summary

• P1357 ("Ignition monitor pulse width not defined") is not a universal, standard OBD-II code; its exact meaning and testing procedure can vary by vehicle. Use OEM service information and any OEM-supplied diagnostic procedures to confirm the exact fault and steps. support a general understanding that DTCs monitor ignition-related parameters and that ignition monitor-related codes may arise from hardware (coils, wiring, sensors) or software/ECU monitoring issues. When diagnosing, prioritize a methodical approach focusing on ignition hardware, wiring/grounds, sensors, and ECU software, while keeping in mind the OEM-specific mappings for P1357.

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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