Check engine light with trouble codes 12. 43 and 53. Hard starting won't idle. Cooling fan will not come on either. 40K miles and was running great before. Thanks.

Welcome to AF. Try "tap testing" the ecm, they were troublesome from day one. Code 53 is a high charging voltage surge, this could damage the pcm, check your charging system also.

12 is not a trouble code. It is the start/stop code.
I believe 43 is a rich or lean O2 sensor, not to say it is bad though.
Are you sure the cooling fan will not run? It should kick in at about 210`
The fan is not related to your problem, however.
Check the basics such as vacuum leak, EGR valve, spark plugs, etc...
Let us know what you find.

Found a service note stating that the fan shuts down when code 53 is set due to 17.1 volts for 2 seconds or less than 10 Volts for 240 seconds. Right now I'm chasing the charging system and wiring to the ECM for an answer.

Thanks for the input as they all help!:cool:

Code 43 was a bad connector at the knocks sensor. I have ordered a new Temperature switch/sensor (bad) for the cooling fan. I have tap checked the ecm with no results. I am still getting a code 53. I have tested the output voltage of the alternator, its never over 14.3 volts. Also tested the ignition voltage to the ecm and it is within spec. Anyone got any ideas? Please. Richard

Is the original hard start no idle issue still present? Even though the pcm passes the tap test it can still be bad from a voltage spike.

Chasing my tail on this car. I put the new fan temp switch in last night. Started the car and it ran for about 3 minutes at idle and quit. No code set, restarted it and drove it around for 40 minutes during which time I stopped several times and restarted it. Came home and tried to restart it 10 minutes later, wouldn't start. Reset ECM, charged battery (drew 10 amps) and restarted car no problem. ECM? If so, do I use my memcal (prom) with the rebuilt ecm or get a new memcal also? Also, the cooling fan never kicked on but the car never overheated either.

Use your memcal. When it wont start you should check for spark, at minimum.

I put the new fan temp switch in last night
Which switch is this? The coolant temp sensor?
Isn't the fan controlled by the computer? On my '87 2.5L, there is a ecm controlled relay on the inner fender that sends current to the fan.

On the back side of the engine this motor has a Temperature switch that is connected to the ecm for the cooling fan circuit. It also has a temperature sensor over at the thermostat housing connected to the ecm and yes this car has a relay for the fan circuit right front fender location. The relay checked out but I put a new one in for the $8 anyway keeping the other as a spare.

I put a remanufactured ecm in the other night and the car is running perfect.
$88 for the ecm, 1 year warranty. Temperature switch $14.00, relay $8, total $110 plus CA sales tax. Time invested, priceless... Anyway, for now the car seems fixed. Thanks for all the input and suggestions, This place is great!

Richard in San Diego, CA

Well done and thanks for the post back on the results.