P1773 — Engine ECU–Additional Heater CAN Link

P1773 — Engine ECU–Additional Heater CAN Link. P1773 primarily affects communication with the additional heater rather than the engine's cooling system.

For Ford vehicles

CAN connection between engine ECU and additional heater

vehicle

Is it safe to drive?

Auxiliary heat may be unavailable P1773 primarily affects communication with the additional heater rather than the engine's cooling system. The vehicle may still drive, but auxiliary heat could be unavailable, so monitor the engine gauges and use caution in very cold conditions.

Typical symptoms

P1773 is stored as a current, pending, or historical communication fault
The driver requests auxiliary heat, but the additional heater does not activate
The blower runs while the air remains cold because the auxiliary heater never starts
The additional heater may operate intermittently when the CAN connection is disturbed
The climate-control system may not display the auxiliary heater's operating status

Common causes

An open or short circuit in the CAN high or CAN low wiring between the engine ECU and additional-heater controller
Corroded, loose, or backed-out terminals in an engine ECU or additional-heater connector
Loss of battery power or ground at the additional-heater control module
A damaged CAN transceiver or failed communication circuit inside the additional-heater controller
A faulty CAN port or internal network interface in the engine ECU
An improperly programmed or incompatible replacement additional-heater controller

How to diagnose with an OBD scanner

Confirm P1773 with an OBD scanner Connect an ELM327 adapter or use AIScanAuto to read the engine ECU. Confirm whether P1773 is current, pending, or stored, capture freeze-frame information, and check other accessible modules for related CAN communication codes.
Check heater-module power and ground With the ignition on, verify that the additional-heater controller has the supply voltage and ground required by the vehicle wiring diagram. Repair any blown fuse, damaged power feed, or loose ground before continuing.
Inspect the CAN wiring and connectors Trace the CAN high and CAN low circuits between the engine ECU and additional-heater controller. Look for chafing, broken insulation, water intrusion, corrosion, bent pins, or terminals that are not fully seated.
Test the CAN network behavior Using the appropriate wiring diagram and test connections, verify that both CAN lines have normal bias voltage and that the engine ECU and heater controller exchange valid messages. An intermittent connection may require wiggle testing while monitoring the data.
Isolate the heater controller If power, ground, and wiring are sound, perform the manufacturer-specific communication test for the additional-heater module. If the module does not communicate, repair or replace it as required, complete any required programming, and then verify operation.
Clear and verify P1773 After the repair, clear P1773 and related codes with the scanner, request auxiliary heat, and confirm that the heater starts and that P1773 does not return. Clearing a code without correcting the CAN fault is not a repair.

Approximate repair cost

A rough independent-shop estimate for diagnosing and repairing P1773 is USD 180–950, depending on whether the fault requires wiring repair, connector service, module replacement, or programming. These figures are estimates only and vary by region, labor rates, vehicle access, and parts availability.

Common questions

What does P1773 mean?

P1773 identifies a CAN communication fault between the engine ECU and the additional-heater controller; it does not by itself confirm a failed heater core.

Can I continue driving with P1773 stored?

Usually, yes, because P1773 directly concerns the additional-heater network. However, auxiliary heat may be unavailable, so the vehicle should be monitored carefully during cold-weather driving.

Does P1773 always mean the additional heater is completely dead?

No. The heater may operate locally, but the engine ECU may be unable to command it or receive its status because the CAN link has failed.

Will an ELM327 scanner fix P1773?

An ELM327 scanner can confirm and clear P1773, but clearing it does not repair the wiring, power supply, ECU, or heater controller, and the code may return.

P1773 — ---

When your vehicle's computer detects a problem with the sensor and actuator circuits related to P1773, it logs this diagnostic trouble code and illuminates the Check Engine light. The engine control module (ECM) or transmission control module (TCM) constantly monitors electrical signals from various sensors and actuators while you drive. When these signals fall outside the manufacturer-specified range for a certain number of driving cycles, the module interprets this as a fault and stores code P1773. This triggers the warning light to alert you that something needs attention in the affected circuit.

The freeze frame data stored alongside P1773 acts as a snapshot of your vehicle's operating conditions at the exact moment the fault occurred. This recorded data includes engine RPM, load percentage, coolant temperature, vehicle speed, and other relevant parameters. Technicians use this information to recreate the driving conditions where the problem appeared, making it easier to replicate and diagnose the fault. Without this snapshot, tracking intermittent problems would be significantly more challenging.

P1773 indicates an electrical issue rather than a mechanical failure. The fault could originate from damaged wiring, a failing component, poor electrical connections, or problems within the control module itself. Because the code relates to sensor and actuator circuits, the specific symptoms you experience depend entirely on which circuit the module detected the abnormality in. The code alone does not pinpoint the exact failed part—it signals that further electrical diagnosis is required to identify the root cause.

Symptoms of P1773

The Check Engine light remains illuminated after the fault is detected
Noticeable increases in fuel consumption during normal driving
Intermittent operation or complete failure of the affected system or component
The vehicle may enter limp mode, restricting power and performance to protect drivetrain components
Reduced functionality of auxiliary systems controlled by the affected circuit
In some cases, no noticeable symptoms besides the illuminated warning light

Common Causes of P1773

Open circuit or shorted wiring within the affected sensor or actuator harness
Corroded, damaged, or loose electrical connectors that interrupt signal transmission
Poor ground connections at the component or control module
Failed sensor or actuator that no longer operates within specification
Faulty control module driver circuits that cannot properly process sensor signals
Wiring harness chafing from heat exposure or rubbing against body components
Water intrusion into connectors causing short circuits or corrosion

How to Diagnose P1773

Connect an OBD2 scanner to the vehicle's diagnostic port and verify that P1773 is stored in the ECM or TCM memory. Save all freeze frame data before clearing anything—this recorded information shows engine and vehicle conditions when the fault first appeared.
Retrieve any additional stored diagnostic trouble codes. Related codes often point toward the specific circuit or component responsible for triggering P1773. Research Technical Service Bulletins (TSBs) for your specific make and model using your VIN at the manufacturer website or NHTSA.gov, as factory-issued service campaigns may address known issues.
Perform a thorough visual inspection of the wiring harness and connectors associated with the affected circuit. Look for damaged insulation, broken wires, corrosion buildup, bent pins, or connectors that are not fully seated. Many intermittent faults stem from connectors that appear fine but have marginal contact.
Using a multimeter, check reference voltage supply, ground circuit resistance, and signal wire continuity at the component connector. Compare your readings against manufacturer specifications to identify voltage drops, opens, or shorts.
Conduct a wiggle test by gently moving the wiring harness while monitoring live data on the scanner. Any signal dropouts or fluctuations indicate broken wires inside the insulation that only fail under movement.
Clear the code and complete a full drive cycle that recreates the freeze frame conditions—similar speeds, loads, and temperatures. If P1773 returns, you have confirmed a hard failure requiring repair of the identified circuit.

Repair Options for P1773

Repairing P1773 requires addressing whichever component or circuit caused the fault. Common repair approaches and typical costs at independent repair shops include:

Sensor or actuator replacement: The failed component itself may need replacement, costing between $150 and $500 for parts and labor depending on the specific part and vehicle accessibility.
Wiring or connector repair: Damaged wiring can often be spliced and repaired, or connectors can be cleaned and serviced. These repairs typically cost between $80 and $250 depending on labor time and any necessary parts.
Control module diagnosis and repair: If the control module itself has failed, repair or replacement ranges from $300 to $1,000 depending on whether the module can be repaired or requires replacement and programming.

Total Cost to Fix P1773

The total cost to resolve P1773 varies widely based on which component actually failed. Independent shop rates for parts and labor in the United States typically fall into these ranges: sensor or actuator replacement runs $150–$500, wiring or connector repairs cost $80–$250, and control module service or replacement ranges from $300–$1,000. Most P1773 faults resolve in the lower-to-mid cost range since wiring issues and sensor failures are more common than control module failures. Always pursue accurate diagnosis before purchasing expensive components—the control module is rarely the culprit despite being the most expensive possible cause.

Can You Drive with P1773?

P1773 is generally classified as a non-critical fault. Most vehicles remain drivable when this code is stored, though you may experience reduced performance, disabled auxiliary features, or slightly increased fuel consumption depending on which circuit is affected. However, if P1773 appears alongside symptoms such as stalling, failure to start, or warnings related to braking or steering systems, treat the situation as urgent and have the vehicle inspected immediately. Otherwise, schedule diagnosis and repair at your earliest convenience to prevent potential roadside breakdowns.