The low coolant level light was flashing on my Saturn right before i took it in for a smog. The smog tech told me it failed due to a OBD self test failure and warning light on the dash. I replaced the coolant reservoir (level sensor) and that seemed to get rid of my low level warning in the dash panel. When i hooked upan OBD code reader, no codes were shown.I thentook it back for a retest, it failed again because it could not complete the ODB self test and the low level light was flashing again. is there a problem with the computer or something? how do i get it to pass smog?

If it was a new replacement reservoir, I would suspect a defective connector or a wiring problem (broken or shorted cable). If the reservoir was obtained from a wrecking yard, I suspect you might have got a bad one, although a broken or shorted cable is still a remote possibility ...

Please indicate exactly what ODBII codes they failed you for (the text on the inspection report). Also, read the codes at Autozone or similar when the light is flashing and post them here.

Sometimes some of the ODBII test parameters will show up as "not ready" if you have not completed a full drive cycle after a code has been set (and then cleared). You can fail for having too many "not readys" (at least in NJ).

Obviously it sounds like OA has given some sound advice.
Once you get the reservoir issue resolved, and the light goes out, be sure to drive it for a bit before going back for the retest.

Edited by: derf

Was the battery disconnected at any point? This would cause the values for the self test to be erased and you''d need to cpmplet a driving cycle in order to complete the self test.

OBD-II Driving Cycle:

If you have a 96 or newer vehicle you have the OBD-II diagnostic system. This system is constantly monitoring the sensors and solenoids on the engine. If you have replaced the battery, disconnected the battery or cleared the codes after making a repair you will need to do what is called a "Driving Cycle". This will perform a diagnostic on all the systems the computer monitors. This cycle can be done in under fifteen minutes.

To perform an OBDII Driving cycle do the following:

1. Cold Start
In order to be classified as a cold start the engine coolant temperature must be below 50ºC (122ºF) and within 6ºC (11ºF) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.

2. Idle
The engine must be run for two and a half minutes with the air conditioner on maximum and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.

3. Accelerate
Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.

4. Hold Steady Speed
Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.

5. Decelerate
Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.

6. Accelerate
Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.

7. Hold Steady Speed
Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.

8. Decelerate
This will perform the same diagnostics as in step 5. Again, don''t press the clutch or brakes or shift gears.

The test results were as follows (i am only listing the failed areas)...


Functional check: Fail


ECS: System Malfunction Light, Result:Fail


"This vehicle failed the MIL/check engine light due to failure to succesfully complete all OBD self tests."


My coolant level was low, don''t know if air bubbles were still in the system from swapping out the reservoir with a new one (from the dealer) or i have a leak, no puddles when parked. Filling up the reservoir got rid of the warning light.


I did clear the codes just before going into the smog, so i''ll try the drive cycle before going in again.Thanks for all your replies. I''ll let you know how it goes.

Mike thank you for posting the drive cycle details. I''''ve wondered about the specifics for quite some time.

Sw2Cam: can we make the drive cycle details into a sticky?

DerfEdited by: derf