Question about 1998 Chevrolet Blazer

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20 Amp Oxygen fuse in the UBEC keeps blowing. I recently replaced all of the O2 sensors because the Check Engine Light was on and I was getting PO155, PO147, and PO135 codes. Now, the light is out. P

1998 Blazer, 4.3L, 2WD. O2 fuse in UBEC compartment keeps blowing. Wih a circuit light checker connected to positive of battery, I have continuity on one side of fuse terminal and none on the other side. I have recently replaced all three of the O2 sensors with Bosch ones.

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  • thenugman May 17, 2009

    Thanks for responding to my request. The O2 sensors (3) were direct plug ins with no modifications to the wiring harness. If I insert a new 20 amp Oxygen fuse in the OBEC and then turn the key to the ON position, it blows immediately. The Check Engine light is not on and the car runs fine otherwise. I am trying to trace the circuit from both sides of the fuse to see if there is a short but I am having trouble determining where the wires connect either under the hood or inside the drivers compartment. I am wondering what the purpose of the Oxygen fuse is since even with it blown, the truck runs and the Check Engine Light is not on.

    Thanks for any help that you can provide.

  • David Neuberger May 11, 2010

    the O2 sensors that you put in may draw more than what the fuse can handle, where they direct connect or did you have to wire them? think I would just replace with stock repacement parts


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Posted on Jan 02, 2017

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SOURCE: Check Engine Light - O2 Sensor - bank 1 running lean

you should have three oxygen sensors on your car, one for each bank of three cylinders; should be towards the Y pipe on each exhaust manifold. Additionally you should have one on the exhaust pipe before the cadilitic converter.

Posted on Nov 20, 2008

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SOURCE: check engine light come on fault codes PO165 and PO155

Yes sorry but they both should be replaced. 

Posted on Dec 26, 2008

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SOURCE: 1999 Chevrolet S-10 Check Engine Light


Posted on Mar 12, 2009

  • 400 Answers

SOURCE: 98 blazer odometer,temp goes out battery light comes on

sound to me like there a short in a fusable link somewhere and the computer could be involved.

Posted on Jul 11, 2009

  • 2359 Answers

SOURCE: 91 S10 rough idle, stalling ALDL problems

Make sure there is no vacuum leaks.

Vacuum leak at intake manifold and vacuum hose.

Bad Idle Air Control Motor (IAC)

Low compression (170 psi + is OK)

Start cleaning and repair these trouble spots and see is there any improvement.


For more advance DIY'er then you may try this.

Use a can of Berryman carburetor clean to locate the vacuum leak.


This is a 20-30 minutes job.

Vacuum leaks can occur in following locations.

Intake manifold AND/OR vacuum lines.

Intake manifold is not accessible unless the engine head if off.

You can still check the potential leak by spraying some Berryman near the intake manifold.

Listen for rpm increase after you introduce the Berryman (FUEL) at idle.

Do the same starting from the brake booster unit (the round unit) on the drive side fire all.

Carefully listen for increase of RPM right after to spray the Berryman to the potential vacuum spot.

Get a friend to HEAR the RPM increase or monitor for RPM on the tech.

DO NOT AIM the Berryman into any heat source.

PLEASE RATE my answer if it is useful to you.

Posted on Dec 17, 2009

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Buy from Rock Auto.Com & replace

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easy job.

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Why the codes po125 & po135 &po155 keep coming back?

Hi there:

DTC P0125 - Insufficient Coolant Temperature For Closed Loop Fuel Control

The simplest thing to do is to reset the code and see if it comes back.
If the code comes back, the problem is likely going to be the result of the above causes (faulty thermostat, faulty ECT sensor, or a low coolant level).

DTC P0135 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
DTC P0155 - 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)

A code P0135 and P0155 may mean that one or more of the following has happened:

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In order to solve just...
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  • Hopoe this helps.

    Aug 28, 2012 | 1999 Toyota Sienna

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    What trouble code deffanition 147

    DTC P0147 - 02 Sensor Heater Circuit Malfunction (Bank I Sensor 3)
    O2 (Oxygen) sensors contain a heating element that allows the sensor to reach operating temperature quickly. This lowers emissions since it allows the engine to reach closed loop faster and also allows the engine to stay in closed loop at idle. The heater circuit is supplied a 12 V battery feed from the PCM or ignition circuit (depending on model) and a ground. The PCM (powertrain control module) monitors how long it takes for the sensors to become active after engine start-up. If it takes too long for the o2 sensors to reach operating temperature, this P0147 can set.

    For this particular o2 sensor, there may be no noticeable symptoms other than:
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    Potential causes of an P0147 code include:
    Bad o2 sensor heater circuit
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    Possible Solutions:
    Unplug the Bank 1, 3 sensor. With KOEO (key on engine off) use a voltmeter to check for battery voltage present at the o2 sensor connector (PCM side). (You can also do this with a test light. Connect to ground and touch lead to heater circuit supply. Light should illuminate with KOEO) You should have battery voltage present.

    a. If voltage is present, check the ground side of the heater element also making sure a good ground is present. If it is, check for any faulty connections & then replace the o2 sensor. If you don't have a good ground, then there is an open in the ground circuit somewhere that will need to be repaired. Look for wiring harness contact with exhaust components or broken/missing connectors, etc.
    b. If battery voltage isn't present with KOEO, check for a blown fuse supplying the heater elements. You may need to get a wiring diagram for this. If the fuse is blown, you'll need to check for a short to ground on the battery supply circuit before replacing the fuse. If you find none, and replacing the fuse re-establishes battery voltage at the o2 sensor connector, then the o2 sensor may have shorted internally, blowing the fuse. Replace it & recheck. (NOTE: it's possible for an o2 sensor's heater circuit to be open/shorted and the o2 sensor to still function).
    c. If you have no battery voltage present with KOEO and there are no blown fuses supplying the heater circuit, then check for an open on the supply circuit. You can do this by ohming the circuit with the o2 sensor unplugged and the PCM unplugged. Repair and recheck.

    Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

    Thank you for using FixYa, have a nice day.

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    I have a 1996 honda passport V6, the car was scanned and found code p0134. the car runs but after a few minutes of warming the car stalls and backfires runs terrible what can cause those type of problems

    This code refers to the front oxygen sensor on Bank 1. Basically the oxygen sensor is inactive.

    DTC P0134 - 02 Sensor Circuit No Activity Detected (Bank I Sensor 1)

    The powertrain control module (PCM) provides a baseline voltage of about 450 mV on the oxygen sensor signal circuit. When cold, the PCM detects the the internal resistance of the sensor is high. As the sensor warms up the resistance is lowered and it starts producing voltage based on the oxygen content in the exhaust. When the PCM determines that the time it took for the sensor to warm up is greater than one minute or that the voltage is inactive (not reading outside 391-491 mV it views the sensor as inactive or open and sets the P0134 code.

    Potential Symptoms: One or more of the following may occur:
    * Check engine light illumination
    * Poorly running/engine missing
    * Blowing black smoke
    * Poor fuel economy
    * Dying, stuttering

    Causes: A code P0134 may mean that one or more of the following has happened:
    * Bad O2 (oxygen) sensor
    * Bad heater circuit in the O2 sensor
    * Wiring or connector to the sensor frayed / broken
    * Blown heater circuit fuse
    * Holes in the exhaust system
    * PCM failure

    Possible Solutions: The most common fix is to replace the oxygen sensor. But that doesn't rule out the possibility of:
    * Rusted exhaust pipe
    * Inspect wiring & connector(s) for problems
    * Excessive amperage blowing heater fuse (still requires replacement of sensor but also replacement of blown fuse)
    * Replace PCM (only as last resort after all other possibilities are covered.

    Hope helps (remember rated and comment this).

    Jul 15, 2010 | 1996 Honda Passport

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