Tech Tip: Toyota Highlander’s Heater Goes from Hot to Cold on its Own – UnderhoodService

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Technical resources to help diagnose and repair engine-related service issues.
Electronic

Tech Tip: Toyota Highlander’s Heater Goes from Hot to Cold on its Own

A loose control knob potentiometer could cause erratic behavior on a Highlander climate control system.

Underhood Service Staff Writers
By Underhood Service Staff Writers
Published:

Vehicle Applications: 2002 Highlander 3.0L;  2003-’04 Highlander 2.4L; 2004-’06 Highlander 3.3L

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Customer Concern: Intermittent heater operation; the heater will go from hot to cold on its own.

Potential Causes: Loose control knob potentiometer. A loose ­control knob nut allowed the ­ribbon to be stretched, causing a poor connection.

Tests/Procedures:
1. Inspect the temperature ­control knob for a loose mounting nut and damaged wire ribbon.

2. Inspect the wire ribbon attached to the temperature control knob to see if it has come loose.

Tech Tips: Some technicians have been able to repair the damaged wire ribbon and reassemble the control panel to avoid complete control panel replacement.

Courtesy of Identifix.

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Many alternator problems turn out to be nothing more than a bad connection at the alternator or a bad wiring harness.

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By Andrew Markel
Andrew Markel is the director of content for Underhood Service magazine. He has been with Babcox Media for 20 years. He is a technician and former service writer and holds several automotive certifications from ASE and ­aftermarket manufacturers.
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If only battery voltage is present at the battery on a running engine, does this mean the alternator is “bad?” No, it does not. It only means that the alternator is not charging, but does not reveal why. Therefore, it does not point to a faulty alternator. All too often, the alternator is condemned by technicians due to this test alone. The cause could instead be a module that distributes the power to the vehicle and regulates the alternator.

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