P1679 — Engine Oil Pressure Output Circuit Malfunction

P1679 — Engine Oil Pressure Output Circuit Malfunction. P1679 concerns the electrical path used to report oil pressure.

For Ford vehicles

engine oil pressure output circuit

vehicle

Is it safe to drive?

Diagnose Promptly P1679 concerns the electrical path used to report oil pressure. Prompt diagnosis is appropriate, but if an oil-pressure warning is illuminated, the gauge reads low, or mechanical testing confirms poor pressure, stop driving immediately.

Typical symptoms

P1679 is stored in the engine control module, sometimes with a check-engine or oil pressure warning.
The instrument-cluster oil pressure gauge remains at zero or displays a default value while the engine is running.
The displayed oil pressure reading fluctuates, freezes, or does not agree with a mechanical gauge test.
No obvious drivability symptom occurs when the fault is limited to the reporting circuit.
An oil pressure warning, knocking noise, or unusually hot oil occurs if the fault is accompanied by actual low pressure.

Common causes

The engine oil pressure sender, sensor, or pressure switch has failed or drifted out of specification.
An open circuit, short to ground, or short to voltage exists in the oil pressure signal wiring.
Corrosion, damaged terminals, or high resistance in the oil pressure sensor connector prevents a valid signal.
A poor sensor ground, damaged reference circuit, or failed internal control-module driver disrupts the output signal.
Genuinely low oil level or reduced oil pressure from a worn pump or restricted oil passage produces an abnormal circuit condition.
An incorrect or improperly installed oil pressure sending component creates an implausible pressure signal.

How to diagnose with an OBD scanner

Check the oil and warning condition With the engine off, verify the oil level is within the specified range and inspect for leaks. If the oil-pressure warning is illuminated or the gauge shows no pressure, stop driving and arrange immediate diagnosis.
Confirm P1679 with a scan tool Connect an OBD2 scanner, an ELM327-based tool, or an AIScanAuto-compatible scan application and read the engine controller codes. Confirm P1679, inspect freeze-frame and status information, and review live oil-pressure data if the vehicle supports that parameter.
Verify actual oil pressure mechanically A technician should test the engine with a calibrated mechanical oil-pressure gauge at the manufacturer-specified engine speed and oil temperature. If actual pressure is low, correct the oil supply, pump, or restriction problem before treating P1679 as only an electrical fault.
Test the oil pressure circuit Using the vehicle wiring diagram, inspect the sending-unit connector and harness for corrosion, damaged pins, opens, and shorts. Check reference voltage, ground integrity, and continuity. On switch-to-ground designs, also verify the pull-up circuit and correct switch closure.
Validate the sender and control module Test the oil pressure sender, sensor, or switch against its specified resistance or voltage behavior and replace it with a matching component if faulty. Do not replace the engine controller until the wiring, connector, ground, and input signal have been proven correct.

Approximate repair cost

A rough independent-shop estimate is about USD $100-$500 for diagnosis plus wiring, connector, or oil-pressure sensor repair. If actual low pressure requires a pump, lubrication, or engine repair, the total may reach approximately USD $1,500. These figures are estimates, not verified quotes, and vary by region, vehicle, parts, and labor rates.

Common questions

Does P1679 mean the engine oil pump has failed?

No. P1679 identifies the engine oil pressure output circuit, which may include the sender, wiring, connector, ground, or control-module circuitry. A failed pump can create low pressure, but the electrical circuit still requires separate verification.

Can I continue driving with P1679 stored?

Only cautiously if there is no oil-pressure warning, the gauge shows a credible value, and oil level is correct. If pressure is low or unverified, avoid further driving and have the vehicle inspected promptly.

What can an ELM327 or AIScanAuto scan tool show for P1679?

It can confirm whether P1679 is present, display related freeze-frame information, and provide live oil-pressure data on supported vehicles. It cannot by itself prove actual oil pressure or locate every wiring defect.

Should I replace the engine control module for P1679?

Usually not. Mechanical pressure, oil level, the sender or switch, connector condition, wiring continuity, and ground integrity should be checked first. Controller replacement should be considered only after the circuit inputs are confirmed correct.

P1679 — ---

When your scan tool pulls code P1679, the powertrain control module has detected that a sensor or actuator circuit is behaving erratically — the electrical signals falling outside the factory-calibrated acceptable range. The specific fault description reads "---," and the ECM flags this whenever the problem persists long enough to be considered a genuine malfunction rather than a temporary glitch.

Your vehicle's control module constantly watches these circuits while you drive, comparing real-time sensor data and actuator feedback against predefined parameters. Think of it as a constant quality-check: every voltage reading, every ground reference, every signal pulse gets compared to what the engineers determined is "normal" for that operating condition. If readings stray too far from that window across multiple drive cycles, the module locks in P1679, illuminates the Check Engine light, and records a freeze frame snapshot — a detailed record of engine speed, load, temperature, and vehicle speed at the exact moment the fault occurred.

The freeze frame data is your most valuable starting point. It tells you what the engine was doing when the control module decided something was wrong, which narrows down whether you're dealing with a sensor failure, a wiring issue, or something else entirely.

Symptoms

When P1679 sets, you'll typically notice one or more of these conditions:

The Check Engine light remains illuminated after the fault is detected
A particular system (such as an emissions component or auxiliary feature) may stop working entirely or behave erratically
Fuel economy sometimes worsens due to incorrect sensor feedback
In some vehicles, the PCM may trigger a limited-performance "limp mode" to protect drivetrain components
The fault might come and go, making diagnosis tricky if it doesn't reappear during your shop visit
Related systems depending on the affected circuit could show degraded performance

Common Causes

The root cause usually falls into one of these categories, listed roughly from most to least frequently encountered:

Wiring problems — an open circuit, short to ground, or short to power in the affected harness
Connector failure — corrosion buildup, loose pins, or physical damage at the harness junction
Blown fuse — a failed feed fuse feeding power to the circuit
Faulty component — the sensor or actuator itself has failed internally
Poor ground connection — inadequate chassis ground causing erratic voltage readings
Control module driver failure — less common, but the PCM output stage handling that circuit can fail

How to Diagnose P1679

Follow this systematic approach to pinpoint the cause before replacing parts:

Connect your scan tool, retrieve P1679, and record all freeze frame data. Note engine rpm, load percentage, coolant temperature, and vehicle speed — replicate these conditions during your test drive if the fault is intermittent.
Scan for additional codes. Related diagnostic trouble codes often point directly to the failing component. Also search for your vehicle's make, model, and model year on the NHTSA website or your manufacturer's technical service bulletin database — many P1679 occurrences have documented factory fixes or software updates.
Perform a thorough visual inspection of the wiring harness and connectors associated with the affected circuit. Look for chafed insulation, broken strands inside the wire, moisture intrusion, green corrosion on terminals, or any signs the connector hasn't been seated properly.
Measure electrical values at the component harness. Check for proper reference voltage (usually 5V for sensors), verify ground circuit continuity, and confirm the signal wire shows expected values with a multimeter or oscilloscope.
Run the wiggle test while monitoring live data on your scanner. Gently flex the harness and manipulate connectors while watching the parameter readings — any dropouts or wild fluctuations confirm a broken wire or intermittent connection.
Clear the code and complete a full drive cycle that mirrors the freeze frame conditions (same RPM, load, temperature, and speed). If P1679 does not return after several cycles, the issue was likely transient. If it comes back, you've confirmed an active fault.

Repair Options and Costs

Costs vary depending on which component is actually at fault. Labor rates reflect typical independent shop pricing in the United States:

Wiring harness or connector repair: $80–$250 — usually the least expensive fix, involving solder splices, new terminals, or harness replacement sections.
Sensor or actuator replacement: $150–$500 — depending on the part cost and labor time for your specific vehicle.
Control module repair or replacement: $300–$1,000 — required only if the PCM's internal driver circuit has failed, which is relatively uncommon.

A proper diagnosis before purchasing parts is essential. Spending $500 on a new sensor only to discover the real problem was a corroded connector inside the engine harness wastes money and time.

Can You Keep Driving?

For most vehicles, P1679 does not immediately disable the car. You can typically continue driving with reduced functionality or slightly degraded performance. However, treat this as a priority repair if you experience any stalling, no-start conditions, or warnings affecting brakes, steering, or stability systems. Ignoring the code allows the underlying issue to potentially damage related components or leave you stranded.