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U0164 Lost Communication With HVAC Control Module

OBD-II Trouble Code Technical Description

Article by
Randy
Randy Worner
ASE Certified Master Technician

Lost Communication With HVAC Control Module

What does that mean?

This is a generic communication system diagnostic trouble code that applies to most OBD-II vehicle makes and models.

This code means that the HVAC Control Module (HVACCM) and other control modules on the vehicle are not communicating with each other. The circuit most often used to communicate with is known as Controller Area Network bus communications, or simply put, CAN bus.

Without this CAN bus, control modules cannot exchange information, and your scan tool may not be able to get information from the vehicle, depending on which circuit is affected.

The hvac control module is typically located behind the dash, usually in the center of the vehicle, or behind the instrument panel. It receives inputs from a variety of sensors, some hardwired directly to it, most are sent over the bus communications system. These inputs allow the module to control the interior temperature of the vehicle, in this case for front only or both front and rear passengers.

Troubleshooting steps may vary depending upon manufacturer, type of communications system, number of wires and wire colors in the communication system.

Note: In the case of Nissan & Infiniti vehicles, this code may be referred to as loss of communication with combination meter. Troubleshooting steps would be similar.

Code Severity & Symptoms

Severity in this case would not be an issue due to the module’s backup capabilities. If an electrical issue arises, the module has a backup, and will default to the defrost position, just as a precaution.

Symptoms of a U0164 code may include:

Causes

Typically the causes for this code to set are:

Diagnostic and Repair Procedures

A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix put out by the manufacturer and can save you time and money during diagnosis.

First, note if there are any other diagnostic fault codes. If any of them are bus communication related or battery / ignition related, diagnose them first. Misdiagnosis has been known to occur if you diagnose the U0164 code before any of the basic codes have been thoroughly diagnosed and dismissed.

If your scan tool can access fault codes and the only one you get from other modules is the U0164, try to access to the hvac control module (HVACCM). If you can access codes from the HVACCM, then the U0164 code is either intermittent or a memory code. If unable to access the HVACCM, then the U0164 code that the other modules are setting is active, and the problem is there now.

The most common failure is a circuit fault which causes the loss of power or ground to the hvac control module.

Check all fuses that power up the HVACCM module on this vehicle. Check all grounds for the HVACCM. Locate where the ground attaching points are on the vehicle and make sure that these connections are clean and tight. If you have to, take them off, get a small wire bristle brush and baking soda/water solution and clean each one, both the connector and where it connects.

If any repairs were made, clear the diagnostic trouble codes from memory, and see if the U0164 code returns or if you are able to communicate with the HVACCM module. If the code does not return or communication is re-established, then the fuses/connections were most likely your problem.

If the code returns, locate the CAN bus communication connections on your vehicle, most importantly the HVACCM connector, which is usually behind the dash/instrument panel. Disconnect the negative battery cable before unplugging the connector at the HVACCM module. Once located, visually inspect the connectors and wiring. Look for scraping, rubbing, bare wires, burn spots or melted plastic.

Pull the connectors apart and carefully inspect the terminals (the metal parts) inside the connectors. See if they look burned or have a green tint indicating corrosion. Use electrical contact cleaner and a plastic bristle brush if cleaning of the terminals is needed. Let dry and apply electrical grease where the terminals contact.

Before connecting the connectors back to the HVACCM, make these few voltage checks. You will need to have access to a digital volt-ohmmeter (DVOM). Verify that you have power and ground at the HVACCM. Gain access to a wiring diagram and determine where the main powers and grounds come into the HVACCM. Reconnect the battery before continuing, with the HVACCM still disconnected. Connect the red lead of your voltmeter to each B+ (battery voltage) supply coming into the HVACCM connector and the black lead of your voltmeter to a good ground (if not sure, battery negative always works). You should see a reading of battery voltage. Verify that you have good grounds as well. Hook the red lead of your voltmeter to battery positive (B+) and the black lead to each ground circuit. Once again you should see battery voltage at each connection. If not, repair the power or ground circuit problem.

Next, check the two communication circuits. Locate the CAN B+ (or MSCAN + circuit) and CAN B- (or MSCAN – circuit). With the black lead of your voltmeter connected to a good ground, connect the red lead to CAN B+. With the Key On, Engine Off, you should see about 0.5 volts and fluctuating slightly. Next, connect the red voltmeter lead to the CAN B- circuit. You should see approximately 4.4 volts and fluctuating slightly.

If all tests have passed and communication is still not possible, or you were unable to clear the U0164 fault code, the only thing left that can be done is to seek assistance from a trained automotive diagnostician, as this would indicate a failed HVACCM. Most of these HVACCM must be programmed, or calibrated to the vehicle to be installed correctly.

Related U0164 DTC Discussions

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