GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1997 🢒 Catera 🢒 Body and Accessories 🢒 Instrument Panel, Gauges, and Console 🢒 DTC 168 Fuel Gauge Voltage High

Object Number: 242451 Size: LF

Circuit Description

A microprocessor in the instrument cluster sends voltage to the fuel tank sensor contained inside the fuel tank. A float arm attached to the sensor changes position with the fuel level in the tank. The fuel sensor is a variable resistor, as the fuel level changes the resistance of the fuel sensor changes. The instrument cluster monitors changes in the voltage caused by the changes in the resistance of the sensor to determine fuel level.

Conditions for Setting the DTC

The fuel gauge circuit is tested every 100 ms. DTC 168 will set in the following ways:

    • When the circuit is open.
    • Shorted to battery
    • The resistance of the fuel sensor is out of range (more than 350 ohms) for more than 8 seconds.

Action Taken When the DTC Sets
    • Stores a DTC 168 in memory.
    • The fuel gauge pointer will return to the zero position.

Conditions for Clearing the MIL/DTC
    • The resistance must be greater than 350 ohms for 4 seconds to clear the fault in the next monitoring cycle.
    • Conditions for the fault are no longer present.
    • Using a scan tool

Diagnostic Aids
    • If the DTC is a history or intermittent DTC try performing the tests shown while WIGGLING wiring and connectors. This can often cause the malfunction to appear.
    • Visually inspect the harness and harness connectors for the following conditions:
      • Damage
      • Corrosion
      • Water intrusion
      • Adequate terminal tension
      • Mis-routed harness
      • Rubbed through wire insulation
      • Broken wire inside the insulation
    • Before replacing the instrument cluster check all power and ground circuits to the cluster.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. This test determines if the fuel tank sensor has high resistance.

    2.

  2. This test determines if system voltage is present. No voltage may indicate an open circuit.

    3.

  3. It is necessary to isolate the circuit before testing the circuit for a short to B+.

    4.

  4. After a circuit repair is made. The instrument cluster is checked again to see if the DTC resets indicating an internal failure.

Step

Action

Value(s)

Yes

No

1

Was the Instrument Cluster System Check performed?

--

Go to Step 2

Go to Instrument Cluster System Check

2
  1. Disconnect connector C400.
  2. Use a DMM to measure the resistance from terminal C (sensor side) and a good ground.

Is the resistance reading 350 ohms or less?

--

Go to Step 3

Go to Step 4

3

Replace the fuel tank sensor. Refer to Fuel Controls.

Is the replacement complete?

--

Go to Step 11

--

4
  1. Turn ON the ignition switch.
  2. Measure for voltage from the instrument cluster at harness connector C400 terminal C.

Is the voltage within the specified range?

B+

Go to Step 5

Go to Step 6

5
  1. Ensure the ignition switch is in the OFF position.
  2. Disconnect connector C200A.
  3. Measure and record the voltage at C200A terminal 2 (sensor side).
  4. Turn ON the ignition switch.
  5. Measure and record the voltage at C200A terminal 2 (sensor side).

Are both voltage readings within the specified range?

Less than 0.1 

V

Go to Step 7

Go to Step 8

6
  1. Disconnect connector C200A.
  2. Measure for voltage from the instrument cluster at C200A terminal 2.

Is the voltage reading within the specified range?

B+

Go to Step 9

Go to Step 10

7
  1. Ensure the ignition switch is in the OFF position.
  2. Remove the instrument cluster. For the removal procedure refer to Instrument Panel, Gauges and Console.
  3. Disconnect the connector form the instrument cluster.
  4. Disconnect the connector form the Engine Control Module (ECM).
  5. Measure and record the voltage at the instrument cluster connector terminal 20 and a good ground.
  6. Turn ON the ignition switch.
  7. Measure and record the voltage at terminal 20.

Are both voltage readings within the specified range?

Less than 0.1 

V

Go to Step 11

Go to Step 14

8

Locate and repair the short to B+ in CKT PF12.

Is the repair complete?

--

Go to Step 11

--

9
  1. Move related harnesses and harness connectors while monitoring the DMM. If a circuit problem is found repair as needed.
  2. If no circuit problem was found replace and program the instrument cluster.

Was a repair replacement made?

--

Go to Step 11

--

10
  1. Remove the instrument cluster and disconnect the connector. For the removal procedure refer to Instrument Panel Gauges and Console.
  2. Measure the resistance from the instrument cluster connector terminal 20 to C200A terminal 2.

Is the resistance within the specified range?

0-5 ohms

Go to Step 12

Go to Step 13

11
  1. Reinstall connectors and components removed.
  2. Install the scan tool and clear codes.
  3. Recheck for a current DTC 168.

Is a current DTC 168 set?

--

Go to Step 12

Go to Instrument Cluster System Check

12

Replace and program the instrument cluster.

Is the replacement complete?

--

Go to Instrument Cluster System Check

--

13

Locate and repair the open circuit between instrument cluster connector terminal 20 and C200A terminal 2.

Is the repair complete?

--

Go to Step 11

--

14

Locate and repair the short to B+ in CKT PF1 or the circuit that leads to terminal 73 of the ECM. Refer to Engine Controls in Cell 20 for further details on the ECM circuit.

Is the repair complete?

--

Go to Step 11

--