reinstalling my engine harness, i turn the key and no fuel pump priming, my first indication something is wrong. i wait a few seconds and i get “reduced engine power” and a bunch of other messages on the dash. i check codes and there is no communication with pcm. anything you guys can come up with? BCM had communication.

 

Need more details, why were you reinstalling the engine harness, any other work done?

 

yes sir. i bought this car as a project, spun bearing, engine already out, harness already out. harness looked tattered, so i rebuilt the whole thing. i just inspected the ignition switch, looked good. ABS/TC, i have no abs module on purpose.

 

For any single module “no comm” you always check that modules powers and grounds…I see you’re a Tech so you should have access to Alldata or Mitchell or whatever your shop uses to check the PCM pin outs…if all P&G’s are good may be a bad PCM…also remove the “comb” from the Star Connector near the BCM and make sure the one for the PCM is clean…make sure the PCM ground on the engine block is connected…same location as negative battery cable.

 

yessir, i use shopkey. regardless, i have checked power and ground fasteners, as well as cleaning all of them, was wondering if there was any others steps i can take to ensure the PCM is bad. thank you for the information will be back on it after work tomorrow.

 

So you checked powers and grounds with at least a 12 volt incandescent test light ??…a 1 or 2 amp old headlight bulb would be even better…there should be 3 battery and ignition power feeds and 4 grounds if I can remember.

 

so i just drove out to the car as you replied. there is

1 white and black wire grounded to chassis right in front of battery

another ground wire from engine harness grounded on the same spot

negative terminal grounded on the same spot

there is one ground on the passenger side coming out of the harness, i grounded that on the “ground strap”. maf sensor getting 12v. not the reference 5v

 

No, you are checking powers and grounds AT the PCM…watch the video…this is one of 3 pages of the PCM connector view…all PCM/ECM/ECU’s have a battery and ignition feed so as you can see on the C1 connector pin 19 is ignition feed and pin 20 is battery feed…watch the video !!…pin 1 is a PCM ground so when checking power you can use pin 1 as your ground…you can also use battery positive or negative when doing these tests…your shop should have back probes which you should be using to probe the PCM terminals…as far as your MAF sensor you should see 12 volts on the pink wire and 5 volts on the yellow signal wire key ON and if you don’t see 5 volts on the signal wire check other circuits with a 5 volt reference such as TPS sensor APP…if no 5 volts PCM is not “alive” and the car will not start and you will have a no comm…same if 5 volt reference is shorted to ground….are you familiar with “short to ground” testing ??…since you rebuilt this harness you’ll need to double check your work or maybe even sourcing a used harness…being a very young Tech you should learn as much as you can about electrical systems…voltage drop testing, testing solenoids, thermistors, potentiometers etc…you first need a strong basic foundation and build on that…to this day I am still attending any electrical classes online or in person that I can get to…there are many good YouTube channels to learn…Scanner Danner, TST Seminars, Motor Age…do you use a labscope in your shop ??…if not you will NOT be able to diagnose cars quickly and accurately and you will only be guessing…a scope is needed to diagnose todays vehicles.

 

Speaking of electrical training these are some excellent classes with the best instructors in the field…Scot Manna, John Thornton, Bernie Thompson…this is a 2 night 4 hour class but a little steep at $150.00 but well worth it…you don’t learn this stuff turning wrenches !!

 

long story short i connected all the grounds into one thick wire, ran that wire around all the grounds then grounded it once on the back of the passenger side head, and the other where the white and black pcm wire grounds. works perfect no issues. thanks for the help.