C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

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Old May 28, 2025 | 10:23 PM
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I'm showing two H codes on my 95. One is 72 which my understanding is just from the after market radio that was installed. The other is 74 which I'm finding multiple explanations for. Do any of you have information on what 74 indicates?
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Old May 29, 2025 | 11:47 AM
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If the H72 and H74 are in Module 1, H72 is LCD lighting, and H74 is LED lighting. "LCD" is the backlighting in the radio and HVAC displays. H72 should only show up on aftermarket radio installation if the car has C60 MANUAL HVAC controls. In a C60 car, there is no LCD display, so removing the radio leaves no LCD backlighting. << This is the situation where the "resistor fix" applies.

H74 Module 1 are the green LED lights above the buttons. HVAC, Fog Light switch, and the radio. My 92 frequently has 1.H74 set, but not always. I ignore it and clear it.

H74 also exists in Module 4 and Module 9. 4.H74 is TCS circuit Low, and 9.H74 is Low Voltage at the TCS/ABS module.

Knowing, and reporting which module the codes are in is important. But almost no one on here ever does. (One guy took a video of his screen for the entire read-out sequence. I found that incredibly helpful.)

Last edited by IHBD; Jun 3, 2025 at 04:48 PM.
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Old May 29, 2025 | 05:19 PM
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Thanks for the information, I'll pull the codes again and pay attention to what module the 74 shows up under. Not worried about the 72 because the radio was replaced by a Pioneer by the PO. Based on the information you provided it appears that regardless of what Module the 74 shows up in it would not be what is is causing my current starting but stalling seconds later. Do you agree with that?
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Old May 29, 2025 | 06:15 PM
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I agree that none of the possible 72 or 74 DTCs will cause your starts but dies.

I put a response in your other thread. Cheers.
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Old May 30, 2025 | 11:46 AM
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Originally Posted by IHBD
If the H72 and H74 are in Module 1, H72 is LCD lighting, and H74 is LED lighting. "LCD" is the backlighting in the radio and HVAC displays. H72 should only show up on aftermarket radio installation if the car has C60 MANUAL HVAC controls. In a C60 car, there is no LCD display, so removing the radio leaves no LCD backlighting. << This is the situation where the "resistor fix" applies.

H74 Module 1 are the green LED lights above the buttons. HVAC, Fog Light switch, and the radio. My 92 frequently has 1.H74 set, but not always. I ignore it and clear it.
This is the first time I've ever seen these two codes explained thoroughly enough to be a meaningful difinitive explanation. Thanks!
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