P0188 -40f ect
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Joined: Apr 2026
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P0188 -40f ect
Truck started strange - ragged firing it seemed - then smoothed out - or so I though. Drove a bit. When trying to start after a 30 min store visit - just cranked - no indication of any cylinder firing.
NO DTC code and smelled gas. Got it towed home. Started reading and wild guess - crankshaft position sensor. Changed, no work. Still same problem. Looked at books some more and though "just maybe" the engine is getting flooded. (gas smell)
so pulled fuse for fuel pump, bled injectoer feed rail (scharder valve) and it started! Quickly replaced fuse and continued to run. NOW DTC code? nothing????!!! But looking at all the data - saw ECT at -40F Um? It don't get that cold in NC!.
Back to the books - onlyi parts involved is/are the ECM (PCM), wiring, ECT sensor. Check sensor - resistance OK. Left connector off - start engine (pull the fuse again) - starts Ok and DTC P0188. OK - then with engine running check voltage at ECT plug 12+VDC. So, wiring checks good. ECT sensor checks out. ??? All else in live data on scan tool ok - just the ECT -40F - Currently ECM sent out for repair. Hope that resolves problems.
4.6L engine - 196K miles - running FINE till last time started to go somewhere with it.
Posting this as ECT @ -40F is bound to result in to much gas injected at start up - which was proved by pulling fuel pump fuse and bleeding gas injector manifold.
Will update in a week or so when ECM returned from repair. (I HOPE that was/is problem)
NO DTC code and smelled gas. Got it towed home. Started reading and wild guess - crankshaft position sensor. Changed, no work. Still same problem. Looked at books some more and though "just maybe" the engine is getting flooded. (gas smell)
so pulled fuse for fuel pump, bled injectoer feed rail (scharder valve) and it started! Quickly replaced fuse and continued to run. NOW DTC code? nothing????!!! But looking at all the data - saw ECT at -40F Um? It don't get that cold in NC!.
Back to the books - onlyi parts involved is/are the ECM (PCM), wiring, ECT sensor. Check sensor - resistance OK. Left connector off - start engine (pull the fuse again) - starts Ok and DTC P0188. OK - then with engine running check voltage at ECT plug 12+VDC. So, wiring checks good. ECT sensor checks out. ??? All else in live data on scan tool ok - just the ECT -40F - Currently ECM sent out for repair. Hope that resolves problems.
4.6L engine - 196K miles - running FINE till last time started to go somewhere with it.
Posting this as ECT @ -40F is bound to result in to much gas injected at start up - which was proved by pulling fuel pump fuse and bleeding gas injector manifold.
Will update in a week or so when ECM returned from repair. (I HOPE that was/is problem)
5 Year Member
Joined: Dec 2018
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From: Ocean Springs MS
Members on this Forum are very skilled at solving the issues that your truck may be experiencing BUT we need you to fully describe your vehicle and symptoms leading up to this issue such a recent work performed, modifications etc. Maintenance history?
As a minimum – Make, Model, Year, Engine, Trans, 4x4(?), Mileage.
As a minimum – Make, Model, Year, Engine, Trans, 4x4(?), Mileage.
Thread Starter
Junior Member
Joined: Apr 2026
Posts: 8
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Sensor replaced "just for drill" - Both old and new show same resistance and response to heat (boiling water test)
Truck is still stock except for upgraded rear springs and RANCHO shocks all around with added anti-roll bar @ rear.
Only work needed has been alternator/water pump (changed pump as I was 'in there" anyway) and some years ago
new coils and plug wires. Always used Mobile 1 and all filters changed periodically. Changed Master cylinder as
brakes "didn't feel right" - replacement restored feel.
Truck only used for truck type load hauling (Home Depot) and towing a 2 ton trailer.
Truck is still stock except for upgraded rear springs and RANCHO shocks all around with added anti-roll bar @ rear.
Only work needed has been alternator/water pump (changed pump as I was 'in there" anyway) and some years ago
new coils and plug wires. Always used Mobile 1 and all filters changed periodically. Changed Master cylinder as
brakes "didn't feel right" - replacement restored feel.
Truck only used for truck type load hauling (Home Depot) and towing a 2 ton trailer.
Thread Starter
Junior Member
Joined: Apr 2026
Posts: 8
Likes: 5
Folks correct - defective ECT sensor - BUT - what a fracus!!! My 1997 F150 built 1996 October @ Norfolk plant - HAS TWO COOLANT sensors. The one most obivious is the sensor for the Dashboard gauge. The one for the PCM is "hidden" behind the alternator and other plumbing. I changed the wrong sensor not knowing there are two AND they are different resistance curves to boot. So, change of "ECT" did not fix issue. Checked wiring per Ford manual and colors didn't match. ???
But appeared that wires went to correct pins for PCM connector THROUGH an intermediate connector that had corroded terminals as moisture had got into it. Cleaned/re-assembled - still -40F !!!! So pulled PCM to have it tested. Checked out perfect. DRAT! Started reading manuals again and FINALLY spotted the 2ND sensor hiding behind the alternator. Changed it out - fixed! (DUH on me) -
Side note: later in model year Ford changed electronics to use ONE sensor for both PCM and dash gauge. Still, I got off cheaper than if I had taken to dealer.
Side note #2: There are vacuum hoses between the battery and the firewall connector for the PCM. When putzing around - a rotted (!?) rubber connection for some vacuum line just partially disintegrated. Had an intermittant DTC for EGR and also the AC/Heat air director door would not work properly (vacuum operated) - more reading. Finally just started going over the entire engine compartment checking EVERY vacuum hose/line/connection and finally spotted the rotted rubber connection hiding between battery and firewall. All OK now!
Turns out the 'no start' due to PCM thinking -40F so dumping to much fuel when attempting start. "Dang computers!"
I think the vacuum line routes to the gas tank evap hardware - did not see any details on it's routing in Ford manuals.
But appeared that wires went to correct pins for PCM connector THROUGH an intermediate connector that had corroded terminals as moisture had got into it. Cleaned/re-assembled - still -40F !!!! So pulled PCM to have it tested. Checked out perfect. DRAT! Started reading manuals again and FINALLY spotted the 2ND sensor hiding behind the alternator. Changed it out - fixed! (DUH on me) -
Side note: later in model year Ford changed electronics to use ONE sensor for both PCM and dash gauge. Still, I got off cheaper than if I had taken to dealer.
Side note #2: There are vacuum hoses between the battery and the firewall connector for the PCM. When putzing around - a rotted (!?) rubber connection for some vacuum line just partially disintegrated. Had an intermittant DTC for EGR and also the AC/Heat air director door would not work properly (vacuum operated) - more reading. Finally just started going over the entire engine compartment checking EVERY vacuum hose/line/connection and finally spotted the rotted rubber connection hiding between battery and firewall. All OK now!
Turns out the 'no start' due to PCM thinking -40F so dumping to much fuel when attempting start. "Dang computers!"
I think the vacuum line routes to the gas tank evap hardware - did not see any details on it's routing in Ford manuals.
