Volvo Repair: 89 240 DL frazzled?, flash flash flash, example 121

Question
I have a 1989 240 DL 4-DR Sedan w/135K mileage.

It recently started failing to start after it had been driven, then turned off for short trips  (engine would crank, but not turn over).  After knocking the fuel pump a bit, it started.  But...  the catch is... immediately following that start-up, the car's check engine light came on, the water-temp gauge isn't registering any temperature, and the 4 door locks fail to activate when the driver's side door is opened.

Is there something simple we may be overlooking?  This is a car that gets driven 1-2 times per week.  The gas tank is full.  Oil/Fluid changes aren't due for another week or so.  It has been a super reliable car until now...    Help!  Thanks...

Answer
I would check the red cables on the positive battery terminal.I would also check for codes in the engine control unit.



in the engine bay on the drivers side near the strut tower there is a small black box with a wire attached to it.place the wire in the terminal marked 2.turn ignition key on (not started)press the small button for 1 second and the code will be displayed as a series of flashes.a red led displays the codes.the code will be three digits.small pause in between flashes for a single number long pause between flashes for the next number.example 121 will be flash.....flash..flash.....flash.repeat three times or until first code repeats itself.to erase the code after all codes have been checked hold the button for a good 5 seconds then release the light should light steady,then press for another 5seconds.this will erase the codes.  email me the codes and i will tell you what they are..socket 2is the fuel system 6 is ignition.