i have a 97 auto se. check engine light has been coming on sporadically since i bought it 10k miles ago. car runs fine and gets 20-25 mpg. lately it has stayed on more, so i finally got off my butt and checked the codes. it read 0705 (evap system), 0903 (evap canister vent control valve), and 0304 (knock sensor). i read in andre3000's post about the ks, but i don't know what to do with the rest of these codes. can anyone help with this?

rob

 

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.

 

Diagnostic Trouble Code 0705 points to a problem with the Evaporative Emission Control System.

This malfunction is detected when the EVAP control system has a leak or the EVAP control system does not operate properly. (EVAP = EVAPorative emissions.)
Possible causes include...
- incorrect fuel tank vacuum relief valve
- incorrect fuel filler cap
- fuel filler cap vent remains open or fails to close
- foreign matter caught in fuel filler cap
- a leak in the line between the intake manifold and the
EVAP Canister Vacuum Control Valve
- foreign matter caught in the EVAP CVCV
- leaks in the EVAP canister or fuel tank
- leaks in the EVAP purge line (pipe and rubber tube)
- EVAP purge line rubber tube bent
- blocked or bent rubber tube to EVAP control system pressure sensor
- loose or disconnected rubber tube
- EVAP CVCV and circuit
- EVAP Canister Purge Volume Control Solenoid Valve and circuit
- absolute pressure sensor
- tank fuel temperature sensor
- MAP/BARO switch solenoid valve and circuit
- blocked or bent rubber tube to MAP/BARO switch solenoid valve
- O-ring of EVAP CVCV is missing or damaged
- water separator
- EVAP canister saturated with water
- EVAP control system pressure sensor
- refueling EVAP vapor cut valve
- ORVR system leaks

This is a "jackpot" code. It points to so many possible causes as to be almost useless. It may be accompanied by another DTC which is more specific.

 

Diagnostic Trouble Code 0903 points to a problem with the EVAP Canister Vent Control Valve. EVAP = EVAPorative emissions control system. This is the system which seeks to minimize air pollution which results from evaporation (as opposed to incomplete combustion) of gasoline.

The EVAP CVCV is located on the EVAP canister (underneath the vehicle near the left rear tire) and is used to seal the canister vent. It has one hose connection and one two-wire electrical connector. The solenoid in the EVAP CVCV responds to signals from the ECM. When the ECM sends an ON signal, the coil in the solenoid valve is energized. A plunger then moves to seal the canister vent. The ability to seal the vent is a necessary part of the diagnosis algorithms for other evaporative loss system components. This solenoid valve is used only for diagnosis, and usually remains open. When the vent is closed, under normal purge conditions, the evaporative loss system is depressurized allowing "EVAP Control System (Small Leak)" diagnosis. Since this part is used only for brief emissions tests the vehicle will usually start and run well despite a Service Engine Soon warning light on the dashboard.

The EVAP CVCV may be bench tested. Remove it from the vehicle (one hose, one connector, two bolts). Verify that air may pass freely through the valve. Then use a pair of fused test leads to apply 12 volts to the terminals to energize the solenoid. Verify that air does not pass freely through the valve. If the CVCV fails these tests, try cleaning it with WD-40 and compressed air. If this fails to free it up, replace the valve. When you install a CVCV (the original or a replacement) always use a new O-ring.

 

thanks daniel. looks like i have some work to do. a couple more questions for you (or anyone) - what are fused test leads? i take it i can't test the solenoid straight off the battery terminals?
can the 0705 code be triggered by topping off at the gas pump? my wife has done this in the past, but not recently.

rob

 

Fused test leads means a pair of test leads one of which has a fuse in-line. You can make your own fused test leads with some stranded copper wire, four alligator clips, and an in-line fuse holder. The value of fused test leads (as opposed to unfused test leads) is that you are less likely to make big sparks and melt something expensive.

Don't know, I never tried that.

 

I believe that if you re-fill your gas tank while the engine is running, it could cause this or the 0903 code to appear.

 

So it seems the knock sensor code is a common one

i got it a month ago and still can't get rid of it.. hopefully the problem will be fixed in the next two days..
I'll post if i figure it out

Ant

 

we've never filled the gas tank with the engine running.
i haven't had a chance to check anything (per daniel's email), but i reset the ecu after i checked the codes and the check engine light stayed off for ~200 miles until shortly after we got gas again. now it's reading the same 3 codes again.
we got about 26 mpg on this weekend's long road trip (almost all highway miles at 60-75 mph), and no problems with the car.
could this combination of symptoms indicate anything in particular?

rob

 

dont know how revelant this is.. but supposedlly if you dont click the gas cap (turn it tight and then keep going til it clicks) there wont be a good seal or something.. thats what my dealer said.. ??

 

This is correct. The Engine Control Module makes periodic tests of fuel system integrity. A loose or missing fuel filler cap is counted as a leak because it allows gasoline vapors to escape into the atmosphere.

 

Sunday, the MIL light came on with the same 3 error codes (0903, 0304, 0705). The engine is not running any differently and gas mileage, power stayed the same.
I had made it a habit to refuel my car with the engine running. I don't know why. I cleared the light and will make sure I shut off the car. I will monitor and see if it comes back on. I will check the knock sensor just in case.
Any suggestions?

 

This is an unsafe practice because there is a risk of fire. The fueling stations I patronize have signs which prohibit this practice.

 

You are totally right. I don't know what I was thinking, and plus I am a mechanical engineer. Shame on me!