On the PCM side, blue PCM connector, pin 18, solid gray color (no stripe) wire circuit 435. That is the EGR low circuit which an issue on that line (be it the wiring, the PCM or the EGR valve or system performance) will trigger P0401 when it tests that code.
There is also a VERY old TSB that states to make sure you clear the DTCs ANY time the PCM is unplugged, reprogrammed, or if the EGR valve is unplugged or replaced as the PCM has an auto zero function in the PCM for the EGR pintle data
61-65-59: SMU - SECTION 6E - ENGINE CONTROLS - CLEAR DTC'S - (Nov 25, 1996)
"CLEAR ANY DTCS FROM THE VCM ANYTIME AFTER DOING VCM REPLACEMENT/ PROGRAMMING, TURNING THE IGNITION ON WHILE THE EGR VALVE IS DISCONNECTED, OR REPLACING THE EGR VALVE."
Some diagnostic aid notes in the GM diag on P0401 for a 1995 S10 Blazer:
Diagnostic Aids
Notice: In order to prevent further damage if the EGR valve shows signs of excessive heat, check the exhaust system for blockage (possibly a plugged converter) using the procedure found on the restricted exhaust system check. If the exhaust system is restricted, repair the cause; one of which might be an injector which is open due to one of the following reasons:
Stuck
Grounded driver circuit
Check the oil for possible fuel contamination if a stuck open fuel injector is found.
Poor connection or damaged harness - Inspect VCM harness connectors for the following conditions:
Backed out terminal BL 18
Improper mating
Broken locks
Improperly formed or damaged terminal
Poor terminal to wire connection
Damaged harness
Intermittent test - If connections and harness check OK, monitor a digital voltmeter connected between terminal BL 18 and ground while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change.
This biggest difference in a HM oil is in contains some "Seal Conditioner". DEXOS oils and most shelf oils are "Dry" oils which over time harden seals. "Seal Conditioner" is more times than not, an Ester. Addition will soften the seals over time but will not repair one that leaks or has cracked. Esters also provide some cleaning but these HM oils don't contain enough to solve out hard deposits. Just the soft stuff. Also a function of an Ester.
Ester's are not 'allowed' as a 'co-base" by license. Weird, right? A certain amount is allowed as an additive. Bunch of game playing is what it is. It's why HM oils don't have a DEXOS approval.
DEXOS is a license 'with' a specification but is not a specification. Never was, never will be. It's GM's slot machine always paying the house. Use what you like.
Our 2007 Acadia had a stroke basically and the car will not move now (although it starts but the idle is erratic with the RPM's fluttering). I can get into reverse and the car will actually move, but in Drive, the throttle does not respond and the car will only move an inch or two at the most. Gauge messages abound -- the usual suspects. Somewhere in the wiring, something has to have gone horribly awry -- either at the BCM (could be right at the harness plug), under the fuse block where all the wires terminate, or a failed ground (or even a bad BCM). In any case, with the number and type of codes I am getting, I am looking for some additional guidance as I know my issue cannot be unique but one of many that has afflicted other Acadias (and similar varieties). Here is the code list (and there are additional codes as well, but these are the big ones):
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