How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask BigBlock434 Your Own Question
BigBlock434, Chevy Mechanic
Category: Chevy
Satisfied Customers: 291
Experience:  ASE Master certified and 100% General Motors trained in all fields
Type Your Chevy Question Here...
BigBlock434 is online now
A new question is answered every 9 seconds

My 1993 Corvette just started this problem. A few minutes when

Resolved Question:

My 1993 Corvette just started this problem. A few minutes when driving, the "Service ASR" lite comes on steady, also the Security light flashes every 30 seconds or so along with the SYS light. Research on the net has said that a wiring harness connection caused the same issue on a 94. Can you tell me which connectors and their location have wires from both system passing through them? The article said something about an AC connector to the engine.
Submitted: 8 years ago.
Category: Chevy
Expert:  BigBlock434 replied 8 years ago.
Intermittent ASR Service Light On After Start Up
Group Ref.: Brakes
Bulletin No.: 475001
Date: February, 1994






Some owners of 1993-94 Corvettes built before November 24, 1993 (VIN 1G1YZ12J8R5800090) may comment on seeing an ASR service light intermittently immediately after vehicle start up.


Install the MEM-CAL listed below. If an ASR service light is still present, immediately after start-up, further problem diagnosis should be followed using instructions in the service manual.




Parts are currently available from GMSPO.



Labor Operation: T0500

Labor Time: 0.5 hour



© 2009 ALLDATA LLC. All rights reserved.
Terms of Use
Customer: replied 8 years ago.
This is an LT1 not an LT5, with automatic transmission. I do not know what a MEM-CAL is, so answer is of no use to me. Does this address both the security and ASR issues?
Expert:  BigBlock434 replied 8 years ago.
This is for a LT1. A mem/cal is the chip inside the computer. Needs to be changed and computer needs to be reprogrammed at your local dealership.
Customer: replied 8 years ago.
DOES this address both issues???????
Expert:  BigBlock434 replied 8 years ago.
What are the codes set in the computer?
Customer: replied 8 years ago.
The only code that comes up is 28 which is AC clutch and cooling fans.
Expert:  BigBlock434 replied 8 years ago.

Code 28 Diagnostic Chart

Quad Driver Module #3 Circuit Diagram

The ECM controls several components through the use of a "Quad-Driver" module integrated into the ECM. Most devices, such as solenoids or relays, receive battery power through a fused circuit to the ignition, and turn "ON", when the circuit is completed to ground. The "Quad-Driver" consists of several electronic switching circuits that provide the ground connection to complete these circuits and turn the devices "ON".

Each "Quad-Driver" has a fault line that is monitored by the ECM. When the QDM switch for a particular circuit is "OPEN", the voltage at the "sense line" will be high (near battery voltage), and when the device is turned "ON" (circuit completed to ground), the voltage at the "sense line" will drop to zero or near zero volts. When a device is commanded "OFF", the ECM expects the voltage in that "sense line" to be high, and when a device is commanded "ON", the ECM expects the voltage in that "sense line" to go low. The QDM fault detection circuit monitors the voltage in the sense line for each device controlled by the QDM. The ECM will monitor the voltage at the coolant fan and A/C clutch sense lines only when an A/C request signal is present. If the QDM fault detection circuit "sees" a voltage other than what it expects for a device in a particular "ON" or "OFF" state, the fault line status will change, and a Code 28 will set. The fault line signal status can be displayed on a "Scan" tool.

Code 28 will set if the ECM detects the wrong voltage potential in the QDM #3 fault line for 25 seconds. This code does not turn on the "Malfunction Indicator Light" (MIL, also known as the "Service Engine Soon" or SES light.)

Numbers below refer to circled numbers on the diagnostic chart.

This step begins checks to see if the QDM can control its output devices. If relay appears to turn "ON", but the clutch or fan for that relay does not operate, check voltage at relay terminal "E" (relay terminal "A" for compressor clutch relay). Should have battery voltage. If not, check power supply circuit for open or short to ground, or burned fuse.Also check the device itself.
This check can detect a partially shorted solenoid coil which would cause excessive current flow. Excessive current flow to the QDM will be detected as a fault, and set this code. If excessive current flow is detected, a circuit check must be performed to isolate the device from the wiring.
The remaining checks will identify a circuit problem that has caused an excessive current flow or inoperative relay. If a QDM circuit check is done on a relay circuit, it is important to identify and check the relay coil terminals of the harness connector for good connections, to avoid improper diagnosis.
Engine should be idling when monitoring QDM status. Using "Scan" tool, monitor the QDM status while moving the wiring harness and related connectors, including the ECM harness and connector. If the failure is induced, a fault will appear on the display. This will indicate a poor connection or an intermittent "open" or "short" in the wiring harness or connector being "wiggled". Also check for bent pins at the ECM connector and ECM terminals. If code recurs, and there are no apparent wiring or connector problems, replace ECM.
For additional information and test procedures on A/C compressor clutch and engine cooling fans and controls, See: Related Tests and Information\C Charts\Chart C-10 A/C Clutch Control Circuit Diagnosis and See: Related Tests and Information\C Charts\Chart C-12 Coolant Fan Control Circuit

BigBlock434 and 5 other Chevy Specialists are ready to help you