Sheet No.
Issue Date:
Rev B, August 4, 2014
© Bosch Automotive Service Solutions LLC
IAC Signal Tester
The 3053S has a flat 4-pin connector. It
fits 1987 and newer GM vehicles with
Model 700 TBI and PFI fuel systems.
The 3052S has a square 4-pin
connector. It fits 1982 and newer GM
vehicles with TBI and PFI fuel systems.
The IAC Signal Tester is used to check the Idle Air Control (IAC) circuit. There are two different types of
signal testers. Use the signal tester shaped like the connector on your vehicle wiring harness.
Using The IAC Signal Tester With An Idle Air Control/Idle Speed Control Tester (3320)
1. Disconnect the vehicle wiring harness from the IAC on the
throttle body.
2. Connect the Idle Air Control/Idle Speed Control tester to the
IAC motor on the throttle body.
3. Connect the signal tester to the vehicle wiring harness.
Checking The IAC Circuit
1. Start the vehicle. Extend and contract the IAC valve using the controls on the Idle Air Control/Idle
Speed Control tester. Each lamp on the signal tester should flash red and green while the IAC is
cycled. The sequence of the colors is not important.
2. If either light does not flash, check the circuit between the vehicle ECM and the harness connector
for broken wires and poor connections.
If both lights flash and the engine speed does not change when the IAC/ISC tester is operated, the
IAC valve may be defective.
If the circuit between the ECM and the IAC signal testers is good, the ECM may be defective.
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Form No. 103378
Parts List &
Operating Instructions
for:
3052S, 3053S
655 Eisenhower Drive
Owatonna, MN 55060 USA
Phone: (507) 455-7000
Tech. Serv.: (800) 533-6127
Fax: (800) 955-8329
Order Entry: (800) 533-6127
Fax: (800) 283-8665
International Sales: (507) 455-7223
Fax: (507) 455-7063
Website: www.otctools.com
