2001 L100 stuck in open loop

[mangocitadel]

Long time reader, first time writer. I've been reading a ton of posts trying to find my answers, but no luck so I'll post a new question. If I'm re-asking something, sorry, and please point me to a thread.

My 2001 Saturn L100 appears to be stuck in open loop mode, and has been stuck in it since some time during a 2000 mile move to the Pacific Northwest. Below is the list of information I could remember that seems pertinent.

Radiator fans do not kick in as they normally would.
Fans work when powered directly.
Temp Gauge in Dash Cluster operates normally (3/8 is normal operating temperature, 1/2 is overheating).
Fluid does flow from engine to radiator once warm (physical thermostat appears to function properly).
Engine will overheat if not running heater, which I just leave on for now.
Fuel mixture is good at startup, running rich once warm.
No Service engine light/codes.
Checked fuses and relay, they're intact/operational.

The other issue with the car is that the A/C doesn't work (hasn't worked as long as I've had the car/long before the open loop issue). No A/C doesn't concern me, but I've read that a lack of coolant/compression in the A/C system can cause seemingly unrelated electrical issues in some Saturns. Don't know how true that is. So, my understanding is that this it's stuck in the open loop mode, which it's supposed to exit once all parts are up to operating temperature. The most obvious causes of this seem to be the sensors (ECT or one of the 2 O2 sensors) malfunctioning. Does the 2001 L100 have 1 or 2 ECT sensors? I'm planning on replacing the ECT sensor tomorrow, since it's the cheapest part, and I'm fairly sure the car's past due to drain and replace the coolant anyway.
Any suggested next steps after those are tested and/or replaced? Any other culprits in keeping the car stuck in open loop?

[fdryer]

What makes you conclude that your engine is operating in open loop mode all the time? This would turn on the SES indicator and give one or more error codes. Unless you pull all the spark plugs to see black coated ceramic, the only other ways to see rich mixtures would be the black smoke exhaust and/or a strong fuel smell from the exhaust. And your tank runs down sooner, giving less mileage for each tankful. Still convinced of open loop mode?

Our L-series engines haven't inherited the early S-series coolant sensor failures but you can check to make sure yours is the brass one. We use only one sensor. A tell tale indication of the correct sensor will be the rounded shoulder of the main sensor body. The faulty pastic ones have squared shoulders. In the How-to library for pictures of both. Check a few things in the next few steps.

Be sure both 30A cooling fan fuses are intact - remove them for testing if necessary as many overlook fuse checks only to find out much later that fuses were the cause of their problems. Those two 30A fuses supply power to the fan control module; the fcm turns on the fans using a combination circuit to allow different speeds and one or both fans to run. What you may have is a faulty fan control module. Its the black plastic box sitting in front of the battery with a large harness connected to it. This fcm contains several relays that may be worn out or their internal contacts sticking, disabling one or both fans from running. You can try removing it (it slides out of its holster) and rapping it against a work bench table to free up a stuck relay or two and see if any fans turn on when the engine is fully warmed up.

The a/c being inoperative will not affect the engine at all.

[mangocitadel]

The simultaneous new conditions of lack of fan activation and the fuel mixture not correcting properly as the engine warms up are what I was basing the open loop mode on. Does the fan control module affect the air to fuel ratio in some way?

The fuel richness I concluded by the car feeling/sounding/responding normally/peppy at cold start, and once it warms up, becomes delayed in response/less torque, lower engine tone/vibration (as if you EQ'd out the high end of the sound), and a moderate decrease in fuel efficiency since the symptoms (~27 city down to 22 so far, though it hasn't been driven enough tankfuls for the mpg change to really be verified longterm). The exhaust is not exceptionally dark. I forgot to note the (thus far) decreased fuel efficiency in my original post, sorry.

I'm not convinced of anything, but given the information I had, open loop mode seemed logical, as it would explain why both of those symptoms arose at the same time.

I have not checked the plugs since the move. Good should-have-been-obvious thing to check. Will do that tomorrow.

I initially (when I realized the fans weren't kicking in) removed and visually inspected the fan control module to make sure there was no foreign substance or anything melted. All connectors and components were very clean. Have not rapped the fcm against anything yet.

I did check the fuses, they were intact, and tried swapping them out for spares with no change. And tested the relay from jumpers. Nice, solid click each time.

Why are you convinced it's not stuck in open loop mode?

[s3nfo]

Not going into closed loop should kick an SES for emissions system failure. No SES, gotta be going into closed loop unless back O2 sensor is bad and providing closed loop voltages, which would be a seriously unique failure.

[fdryer]

Originally Posted by mangocitadel

.... Does the fan control module affect the air to fuel ratio in some way?

No. Fan control is simply a function of managing coolant temperatures whether running the a/c in hot and humid summers or just to reduce coolant temps according to the a/c pressure switch and coolant temperature sensor. Fan control has nothing to do with engine management.

Originally Posted by mangocitadel

.... The fuel richness I concluded by the car feeling/sounding/responding normally/peppy at cold start, and once it warms up, becomes delayed in response/less torque, lower engine tone/vibration...

That indicates the transition from open loop rich mixtures to closed loop lean mixtures as the O2 sensor comes online to contribute valid signal data for the ecm to determine strict emission control. The O2 sensor needs a minute or more to heat up to its minimum 600F operating temperatures before it can output valid signals so the engine runs in open loop until the O2 sensor gets up to operating temps. All this should be gradual and not as pronounced as you've noticed, indicating something else isn't right but its after entering closed loop mode. Using a reader to monitor engine functions would be the easiest way to observe open and closed loop modes. Removing the plugs for a visual inspection would be the old school (and still reliable) way to see overall fuel mixture/correct plug heat range/wear, all in one moment. Tan colored ceramic indicates normal use, black and/or oily means excess fuel/oil, blistered white ceramic indicates excessive lean mixtures/incorrect plug (heat range).

Originally Posted by mangocitadel

.... and a moderate decrease in fuel efficiency since the symptoms (~27 city down to 22 so far, though it hasn't been driven enough tankfuls for the mpg change to really be verified longterm).

This decrease in mileage is usually associated with winter blend fuel with a drop of a few mpg's.

Originally Posted by mangocitadel

.... I initially (when I realized the fans weren't kicking in) removed and visually inspected the fan control module to make sure there was no foreign substance or anything melted. All connectors and components were very clean. Have not rapped the fcm against anything yet...

It would be difficult to impossible to see stuck relay contacts so rapping the fcm against the bench may unstick stuck relays. The internal contacts are doing all the work of allowing current to the fans and they will arc from normal use. Difficult to see unless the covers are removed. 30 amp fuses suggest heavy start-up currents to each fan. Diodes are also used to absorb reverse current generated when the fans are turned off to prevent arcing across each relay contact. The fcm works silently without fail until something goes wrong and its the only main circuit between the battery and fans. Unfortunately its a dealer only item so maybe a junk yard find can improve chances as well as reduce costs otherwise troubleshooting and repairing the fcm is the last option.

Originally Posted by mangocitadel

.... And tested the relay from jumpers. Nice, solid click each time.

Which relays? Powering what?

[mangocitadel]

On the way to the parts store, the SES light finally came on, gave me a P0420 code, Catalyst efficiency. Aside from the converter failing, is there anything else that's likely to cause this? Different forums disagree about whether it can be caused by an O2 sensor going bad, but since they measure on either side of the converter, it seems a good suspect, and I wouldn't be surprised if the o2 sensors are past their suggested mileage.

If there's a hole in the Cat, screwing up the pressure/mixture, it would be very small, as the car is as quiet as it's ever been, hood up and all. Whole car has surprisingly little rust for living in Wisconsin for 8 years.

If the rear o2 sensor is at all likely as a cause of the p0420 and/or performance issue, are denso or ntk still the recommended brands for relatively cheap replacements?

The connector on the ECT sensor is black and rounded. The Body above the socketed part rounded a bit, so maybe I won't swap that.

And in regards to the relay, whoops, wrong subject, that's from when I diagnosing HVAC stuff, which has a relay in the fuse box, unlike the fan system. I'm going to pull the FCM again to see if I can test the relays onboard, but I doubt it's that user serviceable.

[fdryer]

The fcm isn't user serviceable from the standpoint of most car owners - plug 'n play. Only the one's capable with some electronics/electrical knowledge/experience and inquisitive for self learning may wander into circuitry and play. Once accepting the fact that broke (if found broken) can't get any "broker" can experimenting begin with the possibility of repairs ending in returning a brokem unit back to service again.

As to the P0420, here's the wording verbatim from the FSM;

DTC P0420
Three-way catalytic converter (TWC) efficiency is measured by how well it can store oxygen. The PCM monitors converter efficiency by comparing the voltage values of the oxygen sensor 1 (O2S-1) and heated oxygen sensor 2 (HO2S-2). Under normal operating conditions, the O2S-1 should vary between 10-1065 mV and the H02S-2 should remain relatively steady between 500-800 mV. This steady reading of the H02S-2 indicates a correctly functioning catalytic converter. When all parameters have been met, the PCM will run a 5 second DTC P0420 diagnostic at idle. The PCM will command rich and monitor the time it takes the HO2S-2 to go rich. It will then command lean and monitor the time it takes the H02S-2 to go lean. The longer it takes the H02S-2 to change rich/lean means the converter is storing oxygen and is functioning properly. If the 5 second test fails, the PCM may take several tests during several ignition cycles to set the DTC. DTC P0420 sets when the PCM has determined that the catalytic converter is no longer efficient.

Conditions for Setting the DTC
DTC P0420 will set if the PCM has determined the catalytic converter to be inefficient by using the O2S-1 and HO2S-2 when:

Engine run time is greater than 8 minutes and 50 seconds.
Engine speed is at idle within -75 to +150 RPM of the desired idle speed.
The engine speed is over 1,000 RPM for 35 seconds (auto), or 45 seconds (manual) after achieving closed loop
The engine has not been at idle for more than 47 seconds. Once off idle, the counter resets.
The ECT is between 70-125°C (158-257°F).
The IAT is between -21°C to +80°C (-6°F to +176°F).
The calculated converter temp is between 501-627°C (933-1,161°F).
The vehicle speed is less than 5 km/h (3 mph).
The calculated air flow is less than 8 g/s.
Ignition voltage is greater than 9 volts.
Barometric pressure is greater than 72 kPa.
No cam, CKP, ECT, EVAP, fuel tank pressure, FC relay, fuel injector, fuel trim, HO2S-2, IAT, idle speed, knock, MAP, misfire, O2S-1, PCM internal fault, TP, or vehicle speed DTCs have been set.
DTC P0420 diagnostic is sampled once at idle once the above conditions have been met. If that test fails, the PCM will take more samples during the current ignition cycle or may take more samples up to 6 ignition cycles. The extra sampling is to ensure that a converter has truly failed.

Nothing lasts forever. Miles?

[mangocitadel]

The car's at 145k. The person I bought it from owned it over the main suggested maintenance mileage, and didn't really keep track of what was done, so I'm not sure what was swapped at that point. It's perfectly reasonable that the converter is clogged or otherwise on it's way out, but I think it's a rather large coincidence that the cat would konk out on the same day as when my radiator fans stop working. But I'm apparently the only one. I will talk to the shop on monday about getting the cat tested/replaced if necessary, or maybe buy a pressure kit and test that aspect if there's one cheap in town.

[mangocitadel]

Additionally, if the Cat is clogged, wouldn't performance suffer all the time, not just when the car warms up? Or is there some sort of internal expansion that occurs?

[fdryer]

A clogged cat doesn't display any set symptoms as internal mechanical breakdown of the honeycomb structure falls apart at random. In the end and after some time has passed a clogged catcon will just make the exhaust system constipated; erratic engine running, error codes, misfiring, poor acceleration, no acceleration, not getting up to speed (whatever speed you want), etc.. No expansion occurs as much as a destroyed catcon just falls apart and the pieces block off exhaust flow through the tiny honeycomb passages.

I learned about one clogged catcon from a Mazda RX-7 years ago after tearing apart the four-barrel carburetor (jets clogged) once and having the engine run perfectly for a few weeks. Little did I know that the catcon crumbled and eventually could only run in second gear, out of power. It was an RX-7 mechanic that lead me to this and eventual replacement. This cat con gradually clogged and I thought I did a bad job on the carb. A temporary bypass pipe was installed until the cat came in; the car ran like a raped ape.

[mangocitadel]

That is quite the mental image, fdryer. Just thought I'd update what I can. Pulled the plugs, and they all look relatively normal, a little bit of white, but no buildup. With rent et al having just bled me, the shop is going to have to wait a week or two. Will update again when I head there.