So my 02 blazer has had some problems recently. I'm still trying to figure out how to fix p0135 since I have no power at the 02 sensor but a day or two ago the check engine light turned off. When I turn the car off and then the key to the on position the check engine does NOT light up. If I wait to a few min and turn the key to the on position the CEL DOES come on but when I start the vehicle the light turns off. I have 3 codes

P0135
P0128
P0135

anyone have suggestions on whats going on with my CEL?

 

Light came on today when it I started and continued to stay lit when I was driving and when I turned it off. Really weird

 

P0128 - Engine coolant fails to reach preset target temperature - Does your engine come up to proper temperature?
P0135 - HO2S Heater Circuit Bank 1 Sensor 1 - The wiring diagram is in that link so you should be able test continuity on the fused wire for the heater.

I would start by getting those taken care of and see where that gets you.

The CEL operation is odd. The only thing I can think of is that your codes may be hit or miss and the PCM is detecting them some times and not others. When you read the codes, it is just giving you the stored & pending codes depending on the scanner used, it may not indicate what is a current code.

 

Anyone know how the wiring is actually run to the driver side sensor?I can follow the passenger side wires up to a connector which connects to the computer but for the life of me I can't figure out where or how to check continuity from in the wire from the pcm to the driver side sensor connector.

The diagrams loses me when it asks you to see if test light comes on when checking for power. Well mine doesn't. Then asks to ground the harness too and to see if test light comes on. Well my case it doesn't. Then the diagram says to repair lack of heater ignition circuit. Lol. Easy enough if you knew where the circuit runs in the first place.

 

On my 1998 Blazer the driver side harness for the exhaust comes from the driver side back of the engine. Up to the top of the engine and over to the passenger side of the engine.