0411 ECU Controlling e-fans

[BBPanel]

I just finished wiring my 66 Nova with new harness and Speartech EFI harness. When I power up (ign on position) the vehicle, the 2 fans come on high. I have 2 fans wired with 3 relays for lo and hi operation. I verified the relays working properly by grounding the signal wires independent of the ECU. I assume the ECU takes the temp sensor reading and triggers the lo/hi signal to the relays. Why would the fans come on when the temp is room temperature. Does the fact I have no water in the block have an impact on the temp sensor, e.g. sensing no signal and thinking temp is high/infinite so the hi fan signal is triggered? Thanks. -Bob

[LRT]

What OS (operating system) are you using in the PCM ?

[BBPanel]

Have no idea - can I tell from the label on the ECU?

[LRT]

The label won't help. Do you have tuning software ?

The early Gen 3 truck operating systems (1999, 2000, and some 2001) don't seem to operate electric fans correctly.

The 2002 trucks with OS 12212156 will correctly operate electric fans.

[BBPanel]

No, not yet - I have a scanning tool - will that tell me?

[LRT]

Depends on the scanner. EFILive's Scan Tool will display the OS.

[BBPanel]

Its an Actron - guess I can try and see - will probably be tomorrow though

[BBPanel]

Could not find OS but I found VIN and it translates to a 2002 GMC Sierra 2500HD 2WD.

I take that back - there is a CAL ID - 12212156

[LRT]

The good news is, whoever programmed the PCM for you, used the best OS available for the 512 Kb PCM.

Without tuning software, you can't confirm the fan parameters in the tune, but you can still check a few things.

Using your scanner, check what ECT (engine coolant temperature) and A/C Pressure the PCM is registering when the fan(s) come on.

You mentioned having manually grounded each fan relay individually to confirm the wiring. Try disconnecting the High Fan (Fan 2) relay from the PCM, to determine if the Low Fan (Fan 1) subsequently activates correctly. The High Fan (Fan 2) output pin in the PCM would have originally been configured for A/C recirculation - perhaps this was not changed during the initial tune.

[BBPanel]

Well, the PCM has not been tuned/programmed yet - it is just a take-out - maybe I just got lucky. I will check out the ECT and a/c press tomorrow.
No I didn't ground the relays individually, I grounded the hi and lo signal wires attached to the relay circuit with them disconnected from the PCM - to verify the relay circuit is working correctly and it is.

[LRT]

Generally people disable VATS in the PCM with tuning software to get the engine to run - not sure how yours is actually running.

If this is a stock PCM, then disconnect the High Fan (Fan 2) wire from the PCM - it will be still functioning as A/C Recirculation.

[BBPanel]

Sorry if I wasn't clear - engine is not/has not been running - I said when "ign is on" the fans come on (hi) and it doesn't seem like they should - particularly when everything is at room temp. I'm aware of VATS disable - I'm just checking all of the electrical circuits before I get around to starting the engine.

[Six_Shooter]

It could be a Limp Home Mode function. Older GM ECMs would do that when in LHM (turn the fans on).

[BBPanel]

Well today the scanner won't link up - have no idea why. If its in LHM will it set a code indicating that?

[Six_Shooter]

I'm not familiar with how the '0411 acts exactly when/if it goes into LHM, but on older systems, the only code that MIGHT be set is 51, for incorrect checksum/bad MEMCAL. If that happens all ALDL output stops.

Someone more familiar with the '0411 will be able to respond with absolutes.

[BBPanel]

I may have solved the problem - I had wired in an override switch so I could turn the fans on at any time and it appears I had a short in the switch - after fixing this the fans do not come on when ign is on. Now, is the ECU set temps working correctly is for another day. Thanks all.

[okay]

Have no idea - can I tell from the label on the ECU?

Hi dear
you can know your os number with EFilive
read flash chip with programmer
download and instal EFI live v7.5 web (https://www.efilive.com/latest/cat/download-efilive)
open file with EFIlive
you can see all the iformation about your file image (http://www.gearhead-efi.com/Fuel-Injection/attachment.php?attachmentid=10888&stc=1&d=1471245159)

note : if EFIlive can't open your file , conver file from Little Endian format to BigEndian or visa versa.