Can You Repair An O2 Sensor

Every bit vehicles grow older, at that place comes a point when the oxygen or air/fuel ratio sensor's heater circuit will probably fail. When that happens, the easiest fix is to install a new sensor. Only when the vehicle comes back two days later with the same heater code, what and so?

A local shop chosen me in on just such a instance. The vehicle had come from some other store, which had already replaced the oxygen sensor. The shop that called me also replaced the O₂ sensor. Obviously, replacing the sensor was not the proper fix. The vehicle had repeatedly returned with a code of P0031—O2 sensor B1S1 low electric current flow heater circuit failure (open circuit).

From this indicate on I'll refer to both oxygen sensors air/fuel ratio sensors as O₂ sensors simply. I know they aren't the aforementioned thing, but in this case nosotros're concerned only with the heaters inside both sensor types. And in that respect, they're fundamentally the same.

One pop test is to bank check the amperage of the O_two sensor's heater circuit. This exam confirms that the O₂ sensor'south heater itself is working and would pb you to believe that the vehicle is fixed. But what caused the vehicle to return two days later with the same code? One possibility is that the sensor's heater circuit may be coming on at the wrong fourth dimension.

Permit's think about this. Do we demand the O_two sensor's heater excursion coming on when the engine is non running? Not likely. Nosotros need to go on in mind that the ECM is decision-making the performance of the heater circuit. Likewise, an amp meter can't actually aid locate the source of the trouble; it tin can indicate only that the problem is present at that moment.

Whenever I diagnose electric problems, I similar to develop a quick and uncomplicated style of testing the circuits, if possible. When testing the O₂ sensor's heater excursion, I found using a #7440 incandescent calorie-free bulb and socket very helpful. You connect the light to the vehicle's O₂ sensor heater harness in place of the sensor. The light seedling draws about 1.75A at 12V. This is usually within the operating range of the sensor's heater. This works very well—about 95% of the time.

When you supplant a bad O₂ sensor, cut the sensor off the old harness. Using the old harness volition assist eliminate the possibility of borer into the wrong excursion, a potentially costly mistake. Now connect a female spade connector to each heater wire of the harness. Usually the heater wires on the sensor'southward harness are both either black or white. Next, connect the #7440 bulb and lite socket to the harness.

At this point, the four-wire plug configuration seems to be the most pop type of connector actualization in aftermarket shops. However, oxygen sensors can have five or more wires. These sensors will even so accept two dedicated heater wires.

In one case yous friction match the plug and wiring configuration to the vehicle's O_ii sensor connector, yous're fix to start testing. First, tape the reckoner codes, including freeze frame data. Remember, the freeze frame information shows the driving conditions at the point when the code set. Then clear the codes. Some computer systems will close the O₂ heater circuit off until the codes are cleared.

Now, with the ignition switch off, plug the examination harness with the light into the vehicle's O_ii sensor harness connectedness. The light should remain off until the engine is started. Once the engine is running, the light should come on steady or blink. This is considered normal circuit functioning. As a prophylactic precaution, perform this test for thirty seconds or less. The computer may possibly reset the code.

If the light comes on with the ignition switch off or when the cardinal only is turned on (engine off), and so there'southward a problem with the heater circuit. Y'all should refer to the vehicle's wiring schematic for how that circuit is wired.

The O_two sensor'southward heater circuit is controlled in 1 of 2 ways. First is the positively controlled blazon of circuit. If the O₂ sensor heater excursion's negative wire goes directly to ground, wait for a curt-to-power problem. Usually the heater circuit in this case is controlled by a relay. Remove the relay and retest the excursion. If the light comes on over again, locate the short-to-voltage in the wiring harness with the relay removed. Trace the harness from the O_ii sensor's connection back to the relay. When you're close to the source of the problem, the low-cal may flicker or become off.

There are times when the light volition get out instantly once the relay is removed. The relay itself may be shorted or the relay control circuit may take a problem. Either manner, you need to locate the source of the problem.

Now let's cover the O₂ sensor'southward negatively controlled heater circuit. If the wiring schematic shows the O₂ sensor heater circuit is footing controlled through the calculator, start looking for a curt-to-ground on the sensor's negative command wire. One quick examination is to disconnect the reckoner from the circuit. Make sure you have the ignition switch off and the bombardment disconnected outset. Then reconnect the battery and turn the ignition switch back on. If the wire from the O₂ heater connector to the computer is shorted to ground, the light volition notwithstanding be on. Trace the wiring harness back to the computer while monitoring the light. When you locate the area of the short, the light may again flicker or go off.

In the case I was called in on, the vehicle was a 2000 Jeep 1000 Cherokee with the 4.0L engine. The vehicle's O₂ sensor harness was pinched underneath the valve comprehend at the dorsum of the cylinder head. Fortunately, the sensor's negative heater wire was the but wire in the harness that was involved. The valve cover gasket had recently been replaced.

I of the technicians brought up an interesting question: With the control wire being shorted to ground, why did the computer gear up a code for an open heater circuit?

The computer is looking for 12V on the sensor's negative control wire while the figurer's O₂ sensor heater circuit driver (the power transistor in the figurer) is open up. With the wire being grounded, the O₂ sensor heater excursion came on as soon every bit the ignition switch was turned on. The computer control was bypassed at that point. Therefore, the computer's monitored voltage was goose egg while the circuit driver was still open. The computer is programmed to set a code for an open heater circuit at this indicate. Again, this is where the amp meter reading would lead you to recall the circuit is operating fine.

There will as well be times when the light will remain off with the engine running. In that case, first check for a blown fuse. If the O₂ sensor's heater had shorted out, the fuse may have blown too.

One time y'all determine that the fuse is okay, check for voltage at the O₂ sensor harness connection. The modified test harness with the lite will requite yous easy access to the circuit. Remember, the engine needs to exist running at this point. If the voltage is close to zero on the positive heater wire, then locate the open circuit in the power wire back to the fuse. Again, it may have a relay in the circuit besides. Still, if the O₂ sensor harness voltage shows battery voltage on both heater wires (with the light yet connected), locate the possible open up circuit in the sensor's negative wire. Also be sure to check all computer grounds. There's a possibility that the computer may have a dedicated ground for this excursion. The worst-example scenario at this point would be a blown computer driver.

As I pointed out before, this procedure works nearly 95% of the time. One of the vehicles information technology didn't piece of work with was a 1997 Toyota 4Runner with the V6 engine. In this case there was voltage on both wires to the O₂ sensor heater excursion. Most estimator systems volition too monitor the electric current flow to the sensor. The light's current draw was not within the operating range of this system's heater circuit. Therefore, the computer shut the circuit off to protect the system (particularly protecting the reckoner's circuit drivers).

In situations like this, plug a new sensor into the harness only. I recommend using a new sensor here. There are times when the old sensor will initially work, then quit once the sensor gets hot. That actually could be the problem. This test can be performed without the need to install the new sensor into the exhaust piping or manifold.

Now monitor the voltage on the sensor's negative heater wire. When the vehicle is started, 12V should be present momentarily. And so the voltage will driblet to zero or pulse. When using a lab scope, the pulse will increase in on time, dropping to zero as the heater stays on longer. A DVOM could exist used for this test, only go on in mind that the voltmeter is only averaging the reading. That could be confusing.

Whenever yous supervene upon an oxygen sensor due to a heater code, ever check the circuit operation. The test harness with the light makes checking the circuit quick and easy. This will assist eliminate comebacks and save the store and y'all precious time.

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Source: https://www.motor.com/magazine-summary/diagnosing-o2-sensor-heater-circuit-failures/

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