Pappa Grande

I took along trip from NJ to NC ~550 miles straight through. Yesterday my CEL came on and I got the following two codes:0303 & 0304 Front O2 sensor and knock sensor. My car is a 95 SE 5 spd, with 135,000 miles and no problems up to this point except for a broken window motor and new battery recently. I bought it with 70k, so I don't know what work was done before my ownership.

1. First question and most important - worst case scenario - can I drive back to NJ tomorrow ~550 miles, if these two sensors are damaged/defective? What is the worse that can happen, what will likely happen?

2. If these two sensor's need replacements can you suggest a good place to purchase replacements, reasonable parts prices and any tips on doing this work my self.

Please advise - I'm on vacation(thank goodness with my laptop from work), without tools and hope to return home tomorrow - 8/14.

Matt

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DTC 0303
Diagnostic Trouble Code 0303 indicates a problem with the front Oxygen Sensor on the left cylinder bank. The left bank is also called the front bank. It is cylinders 2,4,6. A normal signal sweeps back and forth between 0.2 volts and 0.8 volts. This malfunction was detected when the Engine Control Module received a signal from the sensor which was a constant value of approximately 0.3 volts.

Possible causes include ...
- Harness or connectors (the sensor circuit is open or shorted).
- Defective Oxygen Sensor



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08-02-2001 04:19 PM Reply to Post Edit/Delete Message IP: Logged


bill99gxe
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DTC 0304
Diagnostic Trouble Code 0304 points to a problem with the Knock Sensor. The KS is attached to the cylinder block. It senses engine knocking using a piezoelectric element. A knocking vibration from the cylinder block is senses as vibrational pressure. This pressure is converted into a voltage signal and sent to the Engine Control Module (The computer).

This malfunction is detected when an excessively high or low voltage from the KS is entered to the ECM. Possible causes include...
- the harness or connector (The KS circuit is open or shorted).
- the KS

The KS may be checked with an ohmmeter.

1) Raise the hood. View the engine from the driver's fender. Look into
the deep valley between the cylinder banks and below the intake manifold.
Identify the KS as a black item fastened to the block by a single vertical
bolt. A wire harness wrapped in black leads toward you, out of the valley.
That is the KS sub-harness.

2) Follow the KS sub-harness to it's nearest connector. This is connector F121.
It is located near the upper right-hand corner of the valve cover of the forward cylinder bank, as viewed from the front of the car.

3) Disconnect F121. You have to do a "press the latch and wiggle and
pull" to disconnect it. F121 has only two pins; if you see more than two
pins, you have the wrong connector. Use a digital ohmmeter capable of
measuring more than 10 Megohms. You want to measure the pins of F121, not
the sockets of the matching connector. Measure the resistance between a
good ground (such as the battery negative terminal) and pin #2 of connector
F121. On my car this is the highest of the two pins, the one closest to
the front of the car. The factory spec is 500 - 620 Kohms.

The manual says you have to remove the intake manifold to replace the KS. However, I think that a person with good dexterity and a 10mm ratcheting box wrench could replace the KS without disturbing the manifold.

Sonic

My first suggestion would be to reset the ECU and see if the CEL reoccurs. At this point, the car will run the way it is back to NJ, but the oxygen sensor is a relatively simple fix, so just get it done if it is at fault.

Pappa Grande

medicsonic - thanks, I reset the CEL - but haven't driven long enough to see whether it has come back on.

One more tid bit - during my trip I filled up with gas in virginia (does virginia have different gas than NJ?), and I drove ~100 feet with the gas cap off (because I'm spoiled with full serve gas stations in NJ) to the Mcdonalds next door and then put the cap back on (tightly). I understand that this can also cause a CEL to go on...

Sonic

This is true, but that would not set off either of those codes. Please drive the car and see if it returns.

Pappa Grande

Thanks again - I will do so this morning.

Any other suggestions or advice - I'll be leaving shortly.

Daniel B. Martin

135K miles is a reasonable lifetime for an Oxygen Sensor. Assuming that sensor is original equipment, it is time to replace it. Consider replacing both front sensors if they are the same age.

A loose or missing fuel filler cap causes the Engine Control Module to think there is a fuel system leak. However, this is a two-trip logic failure. Your one-time experience should not trigger the Check Engine Light or store a Diagnostic Trouble Code.

DTC 0304, the Knock Sensor, is unusual in that it does not turn on the CEL. You may have been riding around with that code for weeks or months without knowing it. I suggest you replace one or both front Oxygen Sensors and reset the ECM. That may resolve all the problems. You may also notice improved throttle response.

Pappa Grande

I got home with no problems. The CEL has not turned on again, but regardless I'll look into replacing both front o2 sensors. Has anyone done this recently - any advice about the installation?

Thanks everyone.
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Sonic

My advice, buy a Chilton's or Haynes manual. They are EXCELLENT references, and cover this topic with pictures. About 17 dollars, available at most bookstores or automotive parts stores.