Error codes 15, 21 and 23

Cape Cod GN

Member
Hello all, driving around today and my CEL came on. My scan master G read off codes 15, 21 and 23. The car started missing and running rough as well as the rpm went up to 1500rpm at idle. Additionally the scan master G had a reading of negative 30 degrees coolant and negative 70 for air temp. My TPS was .42 now it reads 4.54. FYI, I replaced my stock dash with a Dakota digital for the GN about a month ago and all was running fine. IDK if this could be related? Any help from all your expertise and knowledge would be a huge help so I don’t start going down a rabbit hole.
 

salvageV6

Daily Driver
ECM wiring check D12 pin for ground return from the coolant sensor and TPS.
There's a ground wire splice for those sensors in the harness called S666 near the front of the left valve cover.
 
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salvageV6

Daily Driver
That sensor ground is a stand alone wire from D12 at the ECM for those 5V powered sensors. Did you tie D12 or the wires at the TPS or coolant sensor to the new dash for any reason?
 

Cape Cod GN

Member
That sensor ground is a stand alone wire from D12 at the ECM for those 5V powered sensors. Did you tie D12 or the wires at TPS or coolant sensor to the new dash for any reason?
Savage V6, FYI I drove it twice during
That sensor ground is a stand alone wire from D12 at the ECM for those 5V powered sensors. Did you tie D12 or the wires at the TPS or coolant sensor to the new dash for any reason?
hi SavageV6. FYI, this happened twice when I was driving through a heat wave. It was around 95-100 degrees. So I’m thinking it’s a connection that’s being affected in the engine compartment. Do you know which plug on the wiring harness has TPS sensor, air temp and coolant temp all connecting to? I’m thinking because of heat sync that this could be the issue. I do see a large plug under the throttle body drivers side. I was thinking I could wrap in a heat resistant sleeve. Thank you.
 

salvageV6

Daily Driver
You need to verify the ground goes from each sensor back to the D12 connector on the ECM plug.
Ohm meter, car off, ECM unplugged one lead on D12 the other lead on each sensor ground that gave you the codes, should read below 1 ohm. Since you had 3 codes at once I would suspect the grounds are intermittant at the splice S666 or at the ECM connector itself. Here's some pics.
20220813_191603.jpg
20220813_191645.jpg
20220813_191859.jpg
 

Pronto

Believe nothing you hear and half of what you see.
Your coolant sensor could be flaky as well. Years ago I had the happen to a Chevy pu I had. It was reading -30* and dumping fuel in like a mofo.
 
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