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Pete, Auto Service Technician
Category: Chevy
Satisfied Customers: 24141
Experience:  14 years GM dealer Technician.
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I have a 1997 GMC Sonoma. I am getting no codes and CEL. My

Customer Question

I have a 1997 GMC Sonoma. I am getting no codes and CEL. My Innova scan tool has the HTR, EGR, and EVAP light flashing. I have done the "drive cycle" for at least 500 miles now and still getting this. What do I need to do?
Submitted: 2 months ago.
Category: Chevy
Expert:  Pete replied 2 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Are you trying to get the monitors to run and pass is this what your attempting here?

Let me know,thanks Pete

Customer: replied 2 months ago.
Expert:  Pete replied 2 months ago.

O.k.,if you are clearing codes or resetting the computer or even disconnecting and reconnecting the battery or have a low voltage issue due to a battery fault this resets the drive cycle every time and continues to take longer to get the monitors to run and pass.There is a procedure I have followed several times before in the past to get these monitors to run and pass (or fail if a fault is still present) that will speed up this process.You may have to do this procedure twice in some cases that I post below.If they still do not run and pass I have seen internal PCM (engine and transmission computer) faults with it needing replaced.

Cold Start
The barometric pressure (BARO) is more than 81 kPa.
The engine coolant temperature (ECT) is between (41-86°F).
The intake air temperature (IAT) is between (41-86°F).
The start-up ECT and IAT are within (16°F) of each other.
The battery voltage is between 9-16 volts.
The fuel level is between 15-85 percent.

Important: Whenever the ignition is turned ON, ignition positive voltage is supplied to the HO2S heaters. After verifying the enable criteria, turn OFF the ignition for approximately 5 minutes to allow the sensors to cool before continuing with the test. Once the engine is started, DO NOT turn the engine OFF for the remaining portion of the set procedure.

Turn OFF all of the accessories,
Set the vehicle parking brake.
Verify the transmission is in Park for automatic transmissions and Neutral for manual transmissions.
Start the engine and allow the engine to idle for 2 minutes.

Acceleration at part throttle to (55 mph) with this speed maintained until the engine reaches operating temperature. This may be up to 8 minutes depending on the start up coolant temperature.
Continued operation under these conditions for an additional 6 minutes.

Acceleration at part throttle to (45-55 mph) with this speed maintained for 2 minutes.
Deceleration to (0 mph).
Engine idling for 2 minutes while the following criteria is maintained:
The service brake is depressed.
The automatic transmission is in drive.
The manual transmission is in neutral with the clutch pedal depressed

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete