Showing Codes 12/51/35?

Here's a link to the listing of fault codes for your car:

https://www.2carpros.com/articles/retrieve-trouble-codes-for-chrysler-dodge-plymouth-odb1-1995-and-earlier-car-mini-van-and-light-trucks

Ignore code 12. That just means the ignition switch was turned off.

35 - Radiator fan control relay circuit, open or short detected.
51 - Air/fuel at limit.

To double check that you counted the flashes correctly, the last code should be code 55. That just means it's done flashing codes. If the code numbers are correct, the first clue would be to observe if the radiator fan turns on when it is supposed to. A quick check for that is to turn the ignition switch to "run", (the engine doesn't have to be running), then unplug the two-wire coolant temperature sensor. By default, the Engine Computer will turn on the radiator fan relay and the fan should run. There's a second coolant temperature sensor in the same area. It has only one wire connected to it. That one is just for the dash gauge and doesn't have anything to do with this code. You can find these sensors on or near the thermostat housing at the engine end of the upper radiator hose, right in the middle / front of the engine.

If the fan does not run, turn the ignition switch off, then spin the fan blade by hand to see if the motor has tight bearings. It should coast for a few revolutions. If it stops spinning as soon as you let go of it, the motor will need to be replaced, and expect to find a burned fuse link wire. There's a bundle of them running around the left strut tower right next to the driver's side hood hinge. Most of them are white, but there may be a few orange, green, or black ones in the bundle. They will all be dull-colored. I'll go into more detail about replacing them if it becomes necessary. Don't use regular wire. The insulation on fuse link wires is designed to not burn or melt.

For code 51, you'll need a scanner to view live engine data while the engine is running and warmed up. Once the coolant reaches around 160 degrees, the readings from the oxygen sensor get included in the fuel metering calculations, and the computer makes adjustments to the amount of fuel being sprayed into the engine. This code is saying it has reached the limits of control and can't make the necessary adjustments. The typical things we start looking at include a vacuum leak, high or low fuel pressure and anything else that affects the mixture ratio. Your car uses the OBD1, (on-board diagnostics, version 1) emissions system. Scanners of that era commonly showed fuel mixture with lights or a display showing it switching between "rich" and "lean" about two time per second. Knowing it's stuck in one state would give you an idea of where to start.

Couple things to be aware of. GM fuel pumps almost always start up, then slow down or fail while you're driving, leaving you sitting in a pile of tears on the side of the road. Chrysler fuel pumps fail in the opposite way. It is extremely uncommon for them to stop running while you're driving. They fail by failing to start up, leaving you sitting in the driveway or parking lot. Often banging on the bottom of the gas tank jars them enough to start running, but the permanent failure is in its future. It's due to worn brushes in the motor. Those get worse over time.

When the fuel pump stops running while you're driving, put the pump way down at the bottom of the list of suspects. I've had a burned terminal in a connector for the fuel pump on my friend's Grand Caravan, and on mine the plug wasn't fully seated after I replaced the rusted gas tank, but there's a much more common failure for your engine and the smaller but similar 2.2L. That is a failing distributor pickup assembly. The Engine Computer needs to know the engine is rotating, (cranking or running), then it turns on the Automatic Shutdown, (ASD) relay. That relay powers the injector(s), the ignition coil(s), the alternator field, and the fuel pump or the fuel pump relay, depending on model. The pickup assembly commonly fails by becoming heat-sensitive, then it may work again after it cools down for a couple of hours.

The clue here that most people overlook is they get hung up on the loss of fuel pressure, or they don't hear the pump turn on. You should still hear the fuel pump run for one second when you turn the ignition switch to "run". If you hear that, the pump is okay along with its relay and wiring. When you have a crank / no-start condition, the overlooked clue is to check for spark. If that is missing, suspect the distributor pickup assembly. Those used to have such a high failure rate that many people carried spares in the glove box.

These assemblies can be replaced anywhere rather easily. The photo below shows what it looks like. The distributor is right in front, middle of the engine with a tall black plastic shield in front of it. That keeps rain water off the spark plug wires. Remove two Philips screws to remove that shield, then remove the distributor cap. Lift the rotor off, then the pickup assembly. Reverse that order with the new part and plug it in.

If you find that you do have solid, steady spark during cranking, the pickup assembly is working. Then we'll have to diagnose the fuel system. If it comes to that, I'll post the wiring diagram and give you places to test. You can use a voltmeter, but in this type of circuit, a simple inexpensive test light can be more accurate. If you need them to get started, here's links on how to use each of them:

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Both of these can be found at Harbor Freight Tools. The meter costs $7.00, and the test light about half of that. Walmart and any hardware store have them too, but at a much higher cost. In the article, they're using a voltmeter with the "auto-ranging" feature. That's an expensive feature you don't need. If you need help setting up your meter, I can help with that.