Despite owning this truck for about 10 years, I've only just recently noticed more consciously that there are both a red "Engine" and amber "Check Engine" lights. The "Check Engine" light seems to be coming on and off more frequently lately, but with no real identifiable cause. The red "Engine" light only has only turned on a couple times while running (once warm), staying lit only briefly.

I have pulled codes and get none. I have two different "ANT1" PCM's I use, as originally found on the '94/5 5-speed 4.9's. No difference between the two, and I've opened them both up to check for leaky caps, finding none.

As a starting point, I need to better understand the functions of the two different "idiot lights".

 

The red light indicates a severe problem and should be addressed ASAP. Yellow is something needs attention. I'm sure there are better descriptions but keeping it basic.

 

The Red Engine Lamp is triggered by the coolant temperature sensor, coolant too hot, or the oil pressure switch, low oil pressure. The yellow/amber Check Engine Light (CEL) is triggered by the computer when a fault is sensed.

A diagram from a 1990 model year F-series truck:

 

That answers it, and in this case it's actually not a concern. Why, you ask? I'm pretty sure my thermostat sticks a bit and is slow to open. As a result, the temperature (very) briefly spikes hot when the engine first warms up but then comes right back down to normal and stays there. It's been during those brief hot spikes that I've seen the red Engine light illuminate for a couple seconds. I really need to do a coolant flush and replace the water pump and thermostat, but that will have to wait until another day.

But any thoughts on why there's no stored codes? Obviously I pulled codes before disconnecting power or swapping PCM's.

 

The Red Engine Light is an analog function outside of computer control. The coolant temperature sensor in the diagram is for the temperature gauge/warning module. This is not the Engine Coolant Temperature (ECT) sensor for the computer (PCM).

For an error to be triggered by the PCM the ECT output signal needs to fall below 0.2 VDC which is the equivalent of ~267F. Obviously the warning module's trigger point is well below that threshold.

 

Excellent description of how the two circuits work.

Relative to the amber "Check Engine Light", I would think any time that illuminates a code would get set, no? Certainly that's not happening in my case.

 

Yes, whenever the amber Check Engine Light (CEL) is triggered there should be code in Continuous Memory. If there is no code there, then verify the Keep Alive Memory (KAM) circuit is intact.

 

So a year+ passes and I finally think again about pulling codes with my factory Star II reader. At first I just (again) got a continuous tone, and then I considered, "Am I really doing this right?" As it turns out, I wasn't, and indeed there's a proper power-up order - for me, here's what worked....
1) Connect code reader to car, including additional single wire (I think that's the STI circuit)
2) Power up code reader in "Fast" mode with Hold/Test button "up"
3) Power up car to On position (KOEO)
4) At this point you should be able to toggle through the codes using the arrow buttons on the bottom. I've got a later (ANT1) EEC-IV PCM, so I get 3-digit codes as follows...
332 (R,M) EGR did not open/respond during test or if memory code, did not open intermittently – EVR or PFE
565 (O) Canister Purge 1 solenoid/circuit failure – Solenoids

I'm not really concerned with either of these, but it is interesting that I've only (semi) recently started getting the CEL, which I assume is related to these two codes. It would be nice not to get the CEL, if only so I'll get alerted if something more critical gets triggered. I do still have EGR, and the canister purge solenoid is still present. I wonder if they're both failed?

 

332: So which is it? Engine running or stored in memory?

565 is an active code

So yes. Both could have failed since they are separate systems.

 

Code 332 is most likely a Stored Code since there is no way to command open the EGR valve with vacuum (KOEO). So the definition of did not open intermittently is the most likely correct one.

Code 565 is showing the computer is not sensing the CANP solenoid electrically. Could be an open connection or an open coil in the CANP.

 

Deleted due to poor reading comprehension.

 

Do the pinpoint tests for those codes (in the PCED)
Check the oil pressure with a direct pressure gauge

Your red engine light is coming on due to low oil pressure, not an overheating condition
You can check the ECT voltage to verify how hot the computer thinks it's getting
At .64v the cooling fan will come on if equipped Yours no fan but you should know what that ECT volts are (if concerned about overheating)

 

Proud of you for having a Star tester
It takes money to buy whisky
Talk is cheap without the right scan tool

 

Yes, both are stored codes. It won't be a high priority to address these, but it would be nice not to have the CEL go on (in case something of great importance triggers it and I just continue to ignore it).