Instruments - False Temperature Gauge Reading
SOURCE: KIA Technician Times Volume 6 Issue 2, 2003TITLE: False Temperature Gauge Reading
APPLIES TO: Optima 4 Cylinder
SERVICE TIP:
Some 4-cylinder Optima models may show intermittent high temperature gauge readings, although ECT (Engine Coolant Temperature) readings displayed by Hi-Scan Pro are within normal operating range. This condition occurs most frequently on older and/or higher mileage vehicles. The most common cause of the condition is a voltage drop across the main ground circuit. Excessive voltage drop is the result of high resistance linked to degraded ground contact and heat.
The fault can be verified with a standard digital volt/ohm meter (DVOM) using the following procedures:
^ Select DC voltage and low scale for DVOM used
^ Attach DVOM positive lead to alternator housing and negative lead to negative post of battery
Note: Make certain all DVOM leads are clear of drive belts and pulleys
^ Start engine, turn headlights and A/C on and monitor the voltage reading. A normal vehicle will indicate less than 0.1V
^ Allow the engine to warm up at idle and monitor DVOM voltage and vehicle temperature gauge. If voltage drop increases (typically to 0.4V or more) you will see the temperature gauge move toward the hot/overheated zone. If this occurs, perform the following repair:
1. Remove ground G13 underneath air cleaner box and #2 gauge ground wire at upper starter attachment bolt (see photos)
2. Inspect bolts, threads, wire to terminal connections and terminal ends for corrosion. Clean, solder, or replace terminals/wire assembly as necessary.
3. Clean contact areas on bell housing and body (do not remove paint from G13 location).
4. Reinstall the grounds using locally available plated star-type lock washers between the terminals and the body and the bellhousing.
5. Start the engine and monitor voltage drop using same procedure as before. Voltage drop should be less than 0.1V. Confirm that temperature gauge indicates normal range. If gauge does not indicate normal range, repeat ground cleaning or replace sending unit.