P1631 — Theft Deterrent Fuel Enable Signal Not Received/ B+ Supply To VCRM A/C Circuit Malfunction

P1631 — Theft Deterrent Fuel Enable Signal Not Received/ B+ Supply To VCRM A/C Circuit Malfunction. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: blown fuse feeding the circuit, corroded, loose or damaged connector, poor ground connection.

For Ford vehicles

engine control unit main relay

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 P1631 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 theft deterrent fuel enable signal not received/ B+ supply to VCRM A/C for damage, corrosion, chafing or poor contact.
Subsystem check Run the module's actuator test for the theft deterrent fuel enable signal not received/ B+ supply to VCRM A/C if your scanner supports it — a component that does not respond to a direct command is confirmed faulty.
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 P1631 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P1631 (parts and labor, USD, independent shop rates): Replace the faulty sensor or actuator: $150–$500; Repair wiring or connectors: $80–$250; Control module repair: $300–$1,000. Overall, fixing P1631 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

What are the symptoms of P1631?

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

Will P1631 clear itself?

Sometimes P1631 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.

What does OBD2 code P1631 mean?

How much does it cost to fix P1631?

Replace the faulty sensor or actuator — $150–$500; Repair wiring or connectors — $80–$250; Control module repair — $300–$1,000. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Is it safe to drive with P1631?

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.

The code P1631 triggers when the engine control module detects a problem with the theft deterrent fuel enable signal or the B+ power supply feeding the Variable Relay Control Module (VCRM) air conditioning circuit. This isn't a straightforward open or short circuit — the module's self-diagnostics have flagged a malfunction that could originate in the wiring, the connectors, the affected component itself, or even the control module's internal driver circuits. The fault falls within the powertrain group of OBD2 codes, meaning it involves systems that affect engine operation or emissions.

The VCRM manages various electrical loads in the vehicle, including relay-controlled circuits like certain air conditioning functions. When the theft deterrent system attempts to communicate with the fuel enable circuit through this pathway, a breakdown in that communication chain — whether from power supply issues, signal loss, or control module problems — will set P1631. The ECU continuously monitors this communication and related circuits while the engine is running.

When the module's self-test detects readings that fall outside expected parameters for a sustained period across multiple drive cycles, it stores P1631 and illuminates the Check Engine Light. The freeze frame data saved alongside the code shows the exact engine conditions at the moment of detection — rpm, load, temperature, and speed — which points you toward the conditions most likely to trigger the fault again.

Symptoms of P1631

The Check Engine Light stays illuminated once P1631 sets. The affected system — whether the theft deterrent fuel enable circuit or the VCRM-controlled A/C circuit — may operate intermittently or fail entirely. Some vehicles enter a reduced-power limp mode depending on which component triggered the code. In certain cases, drivers notice higher fuel consumption because the engine runs in an altered state when the system detects a problem.

Common Causes

Wiring problems cause the majority of P1631 codes. Frayed insulation, broken strands inside the harness, or corrosion at connectors create resistance that confuses the module's self-test. Poor ground connections also fit into this category — without a solid reference point, the module cannot accurately measure circuit performance. Internal component failure is another frequent culprit: the theft deterrent fuel enable circuit or VCRM-controlled device can fail outright. Blown fuses feeding the affected circuit will obviously prevent proper operation. Loose or damaged connectors prevent reliable electrical contact. Finally, control module driver faults or software issues within the ECU itself can set P1631 even when the wiring and components are sound.

How to Diagnose P1631

Start by connecting an OBD2 scanner and confirming P1631 is stored. Record the freeze frame data — it tells you engine rpm, load, coolant temperature, and vehicle speed at the moment the fault occurred, which guides your inspection toward the right conditions. Before diving into electrical testing, look up any manufacturer technical service bulletins (TSBs) for this code on your specific make and model — some faults have documented factory fixes or software updates. Perform a thorough visual inspection of the wiring harness and connectors related to the affected circuits, looking for chafing, melted insulation, green corrosion buildup, or loose locking tabs. If your scanner supports actuator tests, command the suspect component to operate — no response confirms a faulty part. Use a multimeter to check reference voltage, ground integrity, and signal continuity at the component connector. While monitoring live data, gently wiggle the harness and connectors; any dropouts or signal interruptions reveal broken wires or intermittent connections. Finally, clear the code, complete a drive cycle that reproduces the freeze frame conditions, and verify P1631 does not return.

Repair Options and Costs

Address the cheapest and most common problems before replacing expensive components. Wiring repair or connector replacement typically costs $80–$250 depending on accessibility and labor time. If testing confirms a failed sensor or actuator in the theft deterrent or VCRM circuit, replacement runs $150–$500 for parts and installation. Control module repair or replacement — necessary only when testing rules out wiring and component faults — ranges from $300–$1,000.

Total Cost Summary

The exact cost to fix P1631 depends entirely on which part has failed. At independent shop labor rates, expect to pay $80–$250 for wiring or connector repairs, $150–$500 for sensor or actuator replacement, and $300–$1,000 for control module service. Most P1631 repairs fall in the $80–$500 range. Spending time on accurate electrical diagnosis before purchasing parts always saves money — the control module is rarely the root cause.

Can You Drive with P1631?

In most cases the vehicle remains drivable with P1631 stored, though one or more auxiliary systems may function improperly or not at all. The fuel enable circuit and VCRM A/C circuit are not typically safety-critical, so the car will start and move under normal conditions. However, if the fault causes intermittent stalling, no-start conditions, or affects brake/steering warnings, treat it as urgent and address it immediately.