ECM Issue on 99-02 Gmt800?
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ECM Issue on 99-02 Gmt800? Hey all,
Just wanting to get some input on an issue ive been having with a project truck of mine, I recently did the efan conversion for my truck and part of the process is pinning 2 wires to the ecm (pin 42 and pin33) for it to work like factory so strangely after doing that and putting the ecm together carefully my truck is having problems idling which never happened before any advice is appreciated.
Just wanting to get some input on an issue ive been having with a project truck of mine, I recently did the efan conversion for my truck and part of the process is pinning 2 wires to the ecm (pin 42 and pin33) for it to work like factory so strangely after doing that and putting the ecm together carefully my truck is having problems idling which never happened before any advice is appreciated.
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From: Ann Arbor, MI
A 99-02 is a "411" PCM with Red and Blue connectors.
On the Blue connector, pin 33 is TTC Brake Switch Signal; pin 42 is Low Speed Cooling Far Relay Control.
On the Red connector, pin 33 is High Speed Cooling Fan Relay Control; pin 42 is TCC Solenoid Valve Control.
So perhaps you were pinning into Blue-42 and Red-33. Did you mix up the colors perhaps?
If you connected something to Red pin 42, you would be (partly?) engaging the torque converter clutch and the engine would not idle.
On the Blue connector, pin 33 is TTC Brake Switch Signal; pin 42 is Low Speed Cooling Far Relay Control.
On the Red connector, pin 33 is High Speed Cooling Fan Relay Control; pin 42 is TCC Solenoid Valve Control.
So perhaps you were pinning into Blue-42 and Red-33. Did you mix up the colors perhaps?
If you connected something to Red pin 42, you would be (partly?) engaging the torque converter clutch and the engine would not idle.
Last edited by mrvedit; May 12, 2025 at 06:52 PM. Reason: typo
Fan Control Wires to the PCM ground the Relays, so if wired correctly they would be to the ground side of the Relay Coil to energize it. Other side would be 12V so if the TCC Brake Switch Signal got some of that 12v it would lock the Convertor up. Red Pin 42 is a ground command.
Then again at this point was the Tune adjusted for the E-Fans?
Then again at this point was the Tune adjusted for the E-Fans?
