Comprehensive diagnostic guide for OBD-II code P0698

Notes

• OBD-II codes prefixed with P0 (P0xxx) are Powertrain codes. This is established in general references on OBD-II. This guides where P0698 fits in the overall code structure, but the exact OEM definition for P0698 can vary by manufacturer.
• The provided open-source entry in OBD2 CODE DEFINITIONS lists an item translated as This specific mapping may reflect a sensor-reference-voltage issue in some OEM contexts, not a universal factory definition for P0698. Therefore, treat P0698 as a powertrain code related to the power-relay/control circuit in many vehicles, but verify against the specific vehicle's service information.

Purpose of this guide

• To help an ASE-level technician systematically diagnose P0698, with a focus on the power-relay control circuit (and related circuits: fuse, wiring, connectors, ground, and PCM outputs), while noting where definitions diverge across OEMs.
• To present symptom-based expectations, step-by-step diagnostic procedures, probable causes with experience-based likelihoods, and repair strategies.
• To emphasize safety and thoroughness, since relay/control-circuit faults can show up in multiple subsystems (fuel pump, starter, ignition, etc.) and may mask other issues if not properly isolated.

1) Potential symptom patterns you might see

• Intermittent no-crank or no-start condition; engine cranks but fails to start when the relay that powers a major subsystem (commonly the fuel pump) does not energize reliably.
• Vehicle starts inconsistently or stalls soon after start due to the power relay not delivering stable power.
• A distinct relay-like click (relay energizing) can be heard or not heard when the ignition is turned to ON, depending on the circuit.
• Symptom set may involve multiple modules that rely on a common power supply (engine control module, fuel pump, and possibly other high-current devices).
• In some reports or OEM mappings, symptoms may appear with related powertrain codes or sensor reference issues if the PCM mismanages the relay control signal.

2) Quick reference: what P0698 generally signals (in absence of a single universal OEM definition)

• P0698 is categorized under powertrain codes and is related to the power-relay control circuit in many OEM frameworks. The exact target relay can differ by vehicle (fuel-pump relay, main engine relay, or an auxiliary power relay). Because OEM definitions vary, the diagnostic steps focus on verifying the relay circuit that is critical to powering the engine/fuel-system and the PCM's ability to energize that circuit. If a manufacturer maps P0698 to a sensor-reference or sensor-circuit issue in their documentation, the diagnostic path should still begin with the relay circuit in question (coil control from PCM, supply voltage, ground, and fuse integrity) and then extend to sensors if relay control is affected by the PCM.
• There is a separate open-source definition mentioning in some contexts, which reinforces the idea that some P0xxx entries link to sensor-reference issues rather than a pure relay fault. Always confirm the exact OEM definition for the specific vehicle.

3) Diagnostic approach (step-by-step)

Goal: determine whether the fault is a faulty power relay, wiring/connectors, fuses, battery/voltage supply, PCM control, or an upstream sensor/ECU condition that is causing the PCM to miscommand the relay.

Preparation and safety

• Safety first: Disconnecting or manipulating fuel-delivery components can be hazardous. If you work near air/fuel lines or hot components, use appropriate PPE and follow shop safety rules.
• Tools needed: OBD-II scan tool, digital multimeter (DMM), 12V power source (for bench-testing relays), a known-good relay of the same type, wiring diagrams for the vehicle, fuse puller, flashlight, and a fuel-pressure gauge if you plan to check fuel-delivery directly.
• Vehicle prep: Ensure the vehicle is in a safe state for testing (engine off, key out if required for some tests; if a live test is needed, follow proper procedures). Do not run prolong tests that could create unsafe conditions.

Initial data gathering

• Scan the vehicle: Confirm P0698 is present and note any other codes, especially P069x (other power-relay codes) and codes related to battery/charging, fuel system, or sensor references.
• Freeze frame data: Check the ignition status, engine temperature, battery voltage, and whether the fault occurs at a specific RPM or load condition.
• Check for any reported symptoms from the customer (no crank, intermittent start, no pump priming, poor acceleration, or intermittent stalls).

Basic electrical checks (start with the obvious)

• Battery and charging: Measure battery voltage with engine off (target ~12.6 V or higher). Measure voltage while attempting to energize the relay (engine cranking or key ON); voltage under load should remain sufficient (typically >12.0 V for reliable relay operation, though many systems tolerate slightly lower values if the draw isn't excessive).
• Fuses and relays: Inspect the fuse associated with the relay circuit; pull and inspect it for corrosion or damage. If there is more than one relay in the same area, visually inspect for heat damage and ensure the correct fuse is being used.
• Relay status: Listen for a distinct click when the ignition is turned to ON/START (some relays energize only when PCM commands them). If there is no click, that suggests a control signal not reaching the relay coil or a failed coil.

Relay circuit testing (coils and contacts)

• Bench-test the suspected relay:
  • Remove the relay and test its coil resistance with a DMM (typical coil resistance varies by relay type; a broad range might be 60-180 ohms, but verify against OEM specs if available).
  • Apply 12 V to the coil and verify the contact side closes (continuity between the common and normally-open contact; output circuit should show continuity when energized).
• In-vehicle relay test:
  • Verify supply on terminal 30 (B+) when ignition ON.
  • Verify coil control signal on terminal 86 (or 85 depending on wiring) from the PCM/ECU; you should see ~12 V when the PCM is commanding energization.
  • Verify coil ground on the other side of the coil (the opposite coil terminal to the control line). Ground should be solid (low resistance to chassis).
  • Verify that the relay contact side (feeding the fuel pump or other device) has a proper supply when the relay is energized. If the pump or device does not receive voltage with the relay energized, the problem may be a wiring harness fault or a problem with the device being powered rather than the relay itself.
• If the relay does not energize with a proper coil signal and proper ground, suspect PCM control output or a source of undervoltage (battery/charging issue, large parasitic draw, wiring resistance).

Power supply and grounds

• Check the supply side (B+) for the relay circuit. A high-resistance connection, corroded terminal, or damaged wiring can prevent proper energization even if the fuse and relay itself are good.
• Check the PCM ground and chassis ground paths associated with the relay circuit. A weak or corroded ground can lead to intermittent energization or PCM misbehavior.

If the relay energizes and powers the intended device, but the engine still won't start or stay running

• Fuel pump/fuel system checks:
  • If the relay energizes and you can hear/measure fuel pump operation but the engine still has issues, test fuel pressure to confirm adequate supply.
  • If the pump is not delivering, check the pump harness, connectors, and vehicle grounds; also check for pressure regulator and injectors if applicable.
• PCM-side considerations:
  • If the relay energizes reliably but the PCM/control output seems unstable, consider a PCM/software issue or internal fault that intermittently commands the relay.
  • Check for PCM sensor faults that could affect power-demand (for example, sensor-reference or supply issues; see note on sensor-reference voltage below).
• Sensor-reference voltage considerations:
  • Some definitions or mappings may tie P0698 to sensor-reference voltage issues (e.g., a low reference voltage on a sensor circuit that could impact PCM output). If sensor-referenced faults are reported or suspected, verify the reference voltage supply to the relevant sensors and the integrity of their ground and signal lines. See the note in the code-definitions section about the open-source mapping to sensor reference voltage.

Cross-check with related codes

• If P0698 appears along with P069x family codes (e.g., P0699, P069A, etc.), that strengthens the case for a relay-control circuit issue.
• If there are sensor-reference issues appearing in the vehicle's fault list, consider testing the relevant sensor reference circuits in addition to the relay circuit.

Functional tests after repair

• Clear codes and perform a controlled test drive or load test to verify that the relay circuit remains energized under expected conditions.
• Re-scan to ensure no new DTCs reappear and that P0698 does not reappear under the same test conditions.

4) Probable causes and rough likelihood (experience-based)

Note: The exact likelihoods can vary by vehicle model and year. The percentages below reflect typical field experience with relay/control-circuit DTCs in powertrain systems.

• Faulty power relay (coil or contacts) or relay internal failure: 40%
• Wiring, harness, or connector issues in the relay circuit (including corroded or loose connections, damaged insulation, or failed pins): 25%
• Battery/charging system or excessive voltage drop causing insufficient coil voltage to energize the relay (or intermittent power supply): 15%
• PCM control output fault (internal fault, software issue, or failing grounds/voltage rails that affect the coil drive): 10%
• Grounding issues (relay ground or engine/PCM grounding problems, poor chassis or ECU ground connections): 5%
• Other (sensor reference voltage issues or OEM-specific mappings, intermittent conditions): 5%

5) Common diagnostic path summary (actionable steps)

• Step 1: Retrieve all DTCs, note any P069x family codes, and review freeze frame data for ignition status and voltage.
• Step 2: Visually inspect the relay, fuse, and wiring for signs of damage, heat, or corrosion.
• Step 3: Perform a bench test of the suspect relay and verify its coil resistance against typical specs; swap with a known-good relay of the same type if possible.
• Step 4: In-vehicle test:
  • Confirm B+ on the relay supply terminal with ignition ON.
  • Confirm PCM is providing a stable control signal to energize the coil.
  • Confirm coil ground integrity.
  • Confirm the relay contacts close and power is delivered to the device (e.g., fuel pump) when energized.
• Step 5: If the relay path appears sound but the engine still has issues, test the device being powered (fuel pump, etc.) and the related powertrain circuits (e.g., fuel pressure, injector operation, crank/cam sensor signals if they influence PCM behavior).
• Step 6: Check for OEM-specific notes: if your vehicle's OEM documentation defines P0698 differently (e.g., a sensor-reference issue), verify sensor supply and reference circuits, including the sensor's ground and wiring to the PCM.
• Step 7: Clear codes and perform a road test to ensure the fault does not reoccur under real driving conditions.

6) Safety and documentation considerations

• Always document observed symptoms, test results, and the exact relay/connector/fuse wiring as found on the vehicle. Include voltage measurements with references (engine off vs. engine on) and the state of the relay during tests.
• If PCM-related faults are suspected, ensure you follow OEM procedures for reprogramming or reflash if applicable and safe.
• After performing repairs, perform a road test to confirm the issue is resolved and the DTC does not return.

7) References and notes

• Structural context: OBD-II defines diagnostic trouble codes; P0xxx are Powertrain Codes. This is the basis for classifying a fault like P0698 within the powertrain category.
• Generic diagnostic approach for powertrain codes is described in the OBD-II sections, which frames the broad areas to test (relay circuits, sensors, PCM outputs, wiring, and fuses).
• Open-source mapping note: An entry in the OBD2 CODE DEFINITIONS set lists a definition translating to This illustrates that some code definitions may map to sensor-reference or sensor-circuit issues rather than a pure relay fault. If your OEM mapping lists a sensor-reference fault under P0698, treat it as a potential related path to verify sensor power/reference voltages and grounds alongside the relay circuit.
• If you must verify the exact OEM definition for a specific vehicle, consult the manufacturer's service information or OEM diagnostic trouble code glossary; the same P0698 label may have different disease mappings by make/model.

8) Summary

• P0698 is a Powertrain/DTC category code associated with the power-relay control circuit in many vehicles. The exact fault mapping can vary by OEM, with some potential mappings including sensor-reference voltage issues in certain definitions. The most robust diagnostic path focuses on the relay circuit: B+ supply, coil control signal, coil ground, relay contacts, and the device being powered (often a fuel pump). If the relay tests pass but the engine still exhibits issues, expand diagnostics to PCM control outputs, battery/charging stability, grounds, and any related sensor-reference circuits per OEM specifics. Always corroborate with OEM service information for the vehicle you're servicing.

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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