shhaker69

this morning when i started my car(1995) the service engine soon light came on. I figured it was due to a oil change coming due. So I had to go into town and i noticed the light going on and off. not at any specific time sometime after 10 mins. sometimes 15. but when the light was off the car ran ruff. I.E. missing lurching. but as soon as the light came on it settled down....any idea what this might be? thanks hans

STL94LT1

Check the code, it will probably tell you.

shhaker69

whats the easiest way to check the code? dealer?......will a hypertech tell me?

STL94LT1

On a 94/95 you can check the codes with a paper clip as follows:

You short pin "12" to pin "4" and turn the ignition switch to "On" without starting the engine.

The speedometer will display any codes using the same protocol as the 1990-1993 model but there are some changes in the designation for the modules plus additional modules are added:

Module "1" is still the CCM module.

Module "4" is now called the PCM module (Powertrain Control Module) because automatic transmission computer control was added to Engine Control Module in 1994.

Module 7 (on the 1996 model only) is the RTD module. (This is the Real Time Dampening module which replaced the Selective Ride Control module in 1996).

Module 9 is the ABS/ASR module number from 1994 through 1996.
Finally, Module "A", the DERM (Dynamic Energy Control Module --- (the air bag control module) will be requested to show any codes.

Just like the 1990-1993 display, you read the codes on the speedometer (big) and read the module number on the trip odometer (small).

A series of dashed lines for instance “ - - -“ indicates no more stored codes for that module.

A code showing as “C12” for the CCM module (module #1) means no codes are stored. So C12 is a good thing to see.

Again, you can cause the codes to repeat by turning the ignition off for five seconds and then back on.

Turn the ignition off and remove the short to restore normal operation.

To clear the codes,

1. With ignition "off" ground terminal #12 of the DLC (use bent paper clip to connect pin 4 to pin 12)

2. Turn ignition "on".

3. Press trip/odo button on the DIC until 1.7 appears in the trip
monitor area of the instrument cluster.

4. Press eng/met button on the DIC & hold until "---" appears in the
speedometer area of the cluster, this will clear CCM DTC'S.


To clear PCM/ECM codes do the following:


1. Press the trip reset button on the DIC until the desired system is displayed. In this case it will be 4.0.

2. Press trip/odo button on the DIC until the desired diagnostic mode(4.7) is displayed on the trip monitor area of the cluster.

3. Press & hold the eng/met button on the DIC until "---" is
displayed in the speedometer area of the cluster, this will clear PCM codes.


To clear ABS/ASR codes do the following:

Same as above but you’re looking for “9.7” on the trip odo

And here are the codes

1994-1995: Diagnostic Trouble Codes
DTC #11: Malfunction Indicator Lamp Circuit.
DTC #13: Bank #1 Heated Oxygen Sensor #1 Circuit:
DTC #14: Engine Coolant Temperature Sensor Circuit Voltage Low.
DTC #15: Engine Coolant Temperature Sensor Circuit Voltage High.
DTC #16: Distributor Ignition System Low Pulse.
DTC #18: Injector Circuit.
DTC #21: Throttle Position Sensor Circuit Voltage High.
DTC #22: Throttle Position Sensor Circuit Voltage Low.
DTC #23: Intake Temperature Sensor Circuit Voltage High.
DTC #24: Vehicle Speed Sensor Circuit.
DTC #25: Intake Air Temperature Sensor Circuit Voltage Low.
DTC #26: Evaporative Emission Canister Purge Solenoid Valve Circuit.
DTC #27: EGR Vacuum Control Signal Solenoid Valve Circuit.
DTC #28: Transmission Range Pressure Switch Assembly Fault.
DTC #29: Secondary Air Injection Pump Circuit.
DTC #32: Exhaust Gas Recalculation.
DTC #33: Manifold Absolute Pressure Sensor Circuit High.
DTC #34: Manifold Absolute Pressure Sensor Circuit Low.
DTC #36: Distributor Ignition System High Pulse.
DTC #37: Brake Switch Stuck On.
DTC #38: Brake Switch Stuck Off.
DTC #41: Ignition Control Circuit Open.
DTC #42: Ignition Control Circuit Shorted.
DTC #43: Knock Sensor Circuit.
DTC #44: Bank 1 LF Heated Oxygen Sensor #1 Circuit Lean.
DTC #45: Bank 1 LF Heated Oxygen Sensor #1 Circuit Rich.
DTC #47: Knock Sensor Circuit Or Module Missing.
DTC #48: Mass Air Flow Sensor Circuit.
DTC #50: System Voltage Low.
DTC #51: EPROM Programming Error.
DTC #52: Engine Oil Temperature Sensor Circuit Voltage Low.
DTC #53: System Voltage Low.
DTC #55: Fuel Lean Monitor.
DTC #58: Transmission Fluid Temperature Sensor Circuit Low.
DTC #59: Transmission Fluid Temperature Sensor Circuit High.
DTC #62: Engine Oil Temperature Sensor Circuit Voltage Low.
DTC #63: Bank 2 RF Heated Oxygen Sensor #1 Circuit Open.
DTC #64: Bank 2 RF Heated Oxygen Sensor #1 Circuit Lean.
DTC #65: Bank 2 RF Heated Oxygen Sensor #1 Circuit Rich.
DTC #66: A/C Refrigerant Pressure Sensor Circuit Open.
DTC #67: A/C Pressure Sensor Circuit Sensor or A/C Clutch.
DTC #68: A/C Relay Circuit.
DTC #69: A /C Clutch Circuit.
DTC #70: A/C Clutch Relay Driver Circuit.
DTC #72: Vehicle Speed Sensor Loss.
DTC #73: Pressure Control Solenoid Circuit Current Error.
DTC #74: Traction Control System Circuit Low.
DTC #75: Transmission System Voltage Low
DTC #77: Primary Cooling Fan Relay Control Circuit.
DTC #78: Secondary Cooling Fan Relay Control Circuit.
DTC #79: Transmission Fluid Overtemp.
DTC #80: Transmission Component Slipping.
DTC #81: Transmission 2-3 Shift Solenoid Circuit.
DTC #82: Transmission 1-2 Shift Solenoid Circuit.
DTC #83: Torque Converter Solenoid Voltage High.
DTC #84: 3-2 Control Solenoid Circuit.(Auto Only).
DTC #84: 2nd And 3rd Gear Blockout Relay Control Circuit.
DTC #85: Transmission TCC Stock On.
DTC #90: Transmission TCC Solenoid Circuit.
DTC #91: One To Four Upshift Lamp(Manual Only).
DTC #97: VSS Output Circuit.
DTC #98: Tachometer Output Signal Voltage Wrong.

shhaker69

wow, thank you. I guess the next question is where are the pins located. I assume they are under the dash. where you plug in the programmer. thanks again!! hans

STL94LT1

Yes.

JAKE

EXCELLENT info. Thanks much for that.

Since losing my FSM Engine Book, I've missed having that info.

Jake

West Point ROCKS!

shhaker69

thank you very much for the info!! you are my hero....ok since you got me this far and i dont want to jack it up anymore than it is. I'm guessing the upper left is 1 and work my way to the right. I will get a book tomorrow.

STL94LT1

shhaker69

thank god you sent a pic of the paper clip...that was my next question....lol. thank you for all the info i'll let you know what i come up with. hans

shhaker69

ok so i went out there this morning and i got a H72 ON 1 and a H44 on 4. I have a feeling the H72 is due to the gear change, but im not sure what DTC #44: Bank 1 LF Heated Oxygen Sensor #1 Circuit Lean means. Im guessing its bad, if they are bad, should i change both of them since im doing it? hans

MikeC4

This is telling you that your O2 sensor on driver side(Left Front) is measuring a "lean" condition for excessive period of time. The PCM will adjust AFR for drivers side bank by adding more fuel(longer pulse width on the driver side FI's), which is most likely causing your drivability issue. Normal O2 operation will oscillate very quickly between lean(~0.1V) and rich(~0.9V). If the O2 sensor measures a "lean" condition for too long, it will report a DTC 44.

A DTC 44 code will be set when the O2 signal voltage remains below 200mV for 50 seconds continuous.

shhaker69

so....whats that mean, fuel injection problem? fuel filter?

MikeC4

If your engine runs good before it goes into "closed" loop then it is more than likely a faulty O2 sensor. You can check by swapping the Left and Right O2 sensors to see if error code shifts to the Right bank.
After you have swapped the sensors, then clear out the error codes before starting engine by disconnecting negative battery terminal for about 30 seconds.

shhaker69

ya when the service engine light is on the car seems to run fine, but when the light goes out the car starts to miss. they dont seem to be very expensive should i just change them both out and see what happens?

MikeC4

If your current O2 sensors have a lot of miles on them, then I would recommend that you change them both. Also, when you get under the car, inspect the wire harness carefully to make sure that they are not touching any part of the exhaust system. There is always the possibility of wires getting shorted due to melted insulation.

MikeC4

just FYI.....there is a seperate light for "Change Oil" that will illuminate on the left side of the digital dash, kind of near the end of your turn signal switch....

shhaker69

thanks for all your help, im going down to pick them up now along with a manual, ive had the car for about a month, so i hope yall wont get too many questions from me. thanks again!! hans

MikeC4

Hey, we were all new vette owners at one time or another....so go ahead and ask away...

shhaker69

thanks, now i have to figure out how im going to get under it. my buddy is a retired mechanic, hes going to come over and help me find the right placement of the jack stands. i hate getting under cars, i wish i had a lift!! thanks for all your help!!