P0689 — ECM/PCM Power Relay Sense Circuit Low

OBD2 code P0689 flags a problem with the sensor and actuator circuits (ECM/PCM power relay sense circuit low). The car is usually drivable while you plan the repair. Common culprits: faulty sensor or actuator of the affected circuit, poor ground connection, control module driver fault.

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P0689 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the ECM/PCM power relay sense for damage, corrosion, chafing or poor contact.
Subsystem check Check for supply voltage at the ECM/PCM power relay sense connector first; then measure resistance from the signal wire to ground — near-zero ohms confirms a short to ground in the harness.
Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P0689 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P0689 (parts and labor, USD, independent shop rates): Repair wiring or connectors: $80–$250; Control module repair: $300–$1,000; Replace the faulty sensor or actuator: $150–$500. Overall, fixing P0689 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Is it safe to drive with P0689?

In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

What are the symptoms of P0689?

Drivers most often notice: Check Engine Light on, increased fuel consumption in some cases, the affected system operates intermittently or not at all, possible limp mode depending on the affected component.

How do I diagnose P0689 myself?

Start with a scan: confirm P0689, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the ECM/PCM power relay sense, and verify the suspect component against live data before buying parts.

What is the most common cause of P0689?

The most common causes are: faulty sensor or actuator of the affected circuit, poor ground connection, control module driver fault.

Will P0689 clear itself?

Sometimes P0689 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

When your vehicle's engine computer detects that a specific circuit is holding voltage far below where it should be, it stores trouble code P0689. This particular code relates to the ECM or PCM power relay sense circuit — essentially a feedback line that tells the computer whether the main power relay is actually turned on and delivering voltage to the engine control module. If that sense circuit drops too close to ground potential, the ECU logs P0689 because it can no longer trust the status of its own power supply.

The powertrain control module continuously monitors the relay sense circuit while the engine is running. It expects a clean signal at a specific voltage level — typically 5 volts or system voltage depending on the vehicle architecture. When something pulls that signal down toward 0 volts, the module interprets this as a fault condition. Several physical problems can cause this: a wire with damaged insulation that shorts against metal, a relay that has failed internally and drags the sense line down, a broken feed wire that supplies no voltage at all, or a corroded connector that introduces excessive resistance. The key point is that the circuit is supposed to sit at a defined voltage, and P0689 means it is sitting far too low.

In practice, this code often points to a wiring issue rather than a failed computer. The sense circuit runs through several connectors between the relay and the ECM, and any of those points can develop problems over time from heat cycling, vibration, moisture intrusion, or simple age. Freeze frame data stored alongside P0689 captures the exact engine operating conditions — RPM, load, temperature, and vehicle speed — when the fault first appeared, giving you a precise snapshot to compare against later during verification testing.

Symptoms

The Check Engine light illuminates and typically stays on until the fault is cleared
Some vehicles experience noticeably higher fuel consumption while the circuit is faulty
The engine may run rough, stall intermittently, or exhibit hesitation under load
Affected auxiliary systems (such as electric fans or secondary air pumps) may stop working entirely
Limp-home mode activation is possible, restricting performance to protect the engine
In rare cases, the engine may not start at all if the ECU cannot confirm relay status

Causes

Wiring shorted to ground — chafed insulation rubbing against metal brackets or body panels ranks as the most frequent culprit
Failed ECM/PCM power relay with internal contacts that pull the sense circuit low
Missing supply voltage to the sense circuit from a blown fuse or interrupted feed wire
Faulty sensor or actuator connected to the affected circuit that drags the signal down
Internal control module driver failure where the ECM itself cannot process the sense signal correctly
Open circuit or broken wire that prevents the sense signal from reaching the ECU
Poor ground connection at the relay or module causing erratic voltage readings
Corroded, loose, or physically damaged connector with high resistance or intermittent contact

How to diagnose

Connect an OBD2 scanner and verify that P0689 is present and active. Record the freeze frame data immediately — this shows you exactly what the engine was doing when the module first detected the fault, which is essential for recreating the failure condition later.
Pull all related diagnostic trouble codes from the vehicle. Codes in the P06xx family often cluster together, and codes pointing to specific sensors or circuits can direct you toward the root cause faster than testing everything blindly. Check for any manufacturer TSBs related to P0689 on your specific make and model by searching the NHTSA database or the automaker's technical portal using your VIN.
Perform a thorough visual inspection of the wiring harness and connectors associated with the ECM/PCM power relay sense circuit. Look for cracked wire insulation, melted sections, corrosion buildup, bent pins, and any signs that connectors have been pulled apart and reassembled incorrectly.
Test for supply voltage at the relay and the ECM/PCM connector. With the circuit powered, measure from the sense wire to a known good ground — if you read near-zero volts when you should see 5 volts or battery voltage, the circuit is being pulled low. Then check resistance from the sense wire to ground; a reading below 1 ohm confirms a direct short somewhere in the harness.
At the component connector, verify that reference voltage, ground, and signal wires all read correctly. A failed sensor or actuator can introduce a dead short that manifests as P0689 at the ECU.
Perform a wiggle test on the harness while monitoring live data on the scanner. Any signal dropouts or glitches point to broken strands inside a wire that appears intact from the outside.
After repairs, clear the code and drive the vehicle through a complete drive cycle that reproduces the conditions captured in the freeze frame. If P0689 does not return, the repair is confirmed.

Repair options

Costs vary based on what actually failed. Shop rates quoted below reflect typical independent repair shop pricing in USD.

Repair or replace damaged wiring and connectors: $80–$250
Control module diagnosis and repair (ECM/PCM service specialist): $300–$1,000
Replace the faulty sensor, actuator, or power relay: $150–$500

How much does it cost to fix P0689?

The total bill depends entirely on which component in the sense circuit is actually at fault. In most cases, the problem is wiring — a straightforward fix that lands at the lower end of the range. Sensor and relay replacements fall in the middle. Computer-level repairs are uncommon but can push costs toward the upper limit if the ECM itself requires service. Expect to pay between $80 and $1,000 for a complete resolution. Spending time on accurate diagnosis before purchasing parts almost always costs less than blindly replacing the most expensive possible component first.

Can you drive with P0689?

Severity is rated short — most vehicles remain drivable after this code sets, though you may notice reduced performance, poorer fuel economy, or an inoperable auxiliary system. If the engine stalls, fails to start, or you receive warnings related to braking or steering assist, stop driving and address the issue immediately. Otherwise, schedule diagnosis and repair at your earliest convenience to prevent the fault from worsening.