ISC Throttle Switch

NOTE: If ISC fails to perform either of these functions, replace ISC.

To test the ISC plunger, use the following steps:

Disconnect ISC connector and connect the jumper harness, see Fig 1 , to ISC.

Fig 1: Identifying Jumper Harness
Courtesy of GENERAL MOTORS CORP.
Connect the jumper wire leading to ISC terminal "C" to 12 volts at the battery or junction block. See Fig 2 .

Fig 2: Identifying ISC Terminal Pins
Courtesy of GENERAL MOTORS CORP.
Apply finger pressure to the ISC plunger, see Fig 3 , (close the throttle switch). Touch the jumper wire connected to ISC terminal "D" to ground until the ISC plunger retracts fully and stops. Immediately remove the ground.

Fig 3: Identifying Retracting ISC Plunger
Courtesy of GENERAL MOTORS CORP.

Do not leave terminal "D" grounded for longer than necessary to fully retract the ISC plunger. If the ISC is stalled retracted for prolonged periods, damage to the ISC will result. Apply finger pressure to the ISC plunger before connecting terminal "D" to ground. Retracting the ISC without pressure on the plunger may cause the internal gears to clash and bind.

CAUTION: Never connect a voltage source to ISC motor terminals "A" and "B" as damage to the internal throttle switch contacts will result.

To extend the ISC plunger use the following steps:

Connect ISC terminal "D" to 12 volts at the battery or junction block.
Connect the ISC terminal "C" to ground until the ISC plunger is partially or fully extended.

If the ISC motor fails to extend, disconnect and reconnect terminal "C" to ground to "bump" the motor from its stalled fully retracted position.

For testing Throttle Switch circuit, check for related diagnostic codes. See SELF-DIAGNOSTICS article.