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Discussion Starter · #1 ·
I have been having trouble with my taurus approximately every two weeks, the car is a 2002 with around 45,000 miles. The car will usually start off by sort of shifting into neutral while driving and then it searches to get back into gear. While doing this the transaxle light will flicker and then the check engine light will come on. When I check the codes that come up, there are 21 codes every time this happens. It seems like pretty much all of the codes are for 5 volt reference sensors. I have already changed the coil pack which I thought may have been shocking the system. Once the codes are cleared in the car I can usually drive it around for about two weeks before this problem happens again. I have also taken the car on some longer drives without having this problem occur at all. This problem has happpened both with the engine warmed up and with the engine cold. I am not sure if this could be an ecm problem or a short in the wirirng harness. Does anyone have any idea of what the problem is, or where I should go from here?
 

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^^^^ +1

I am guessing a loss of 5 v VREF or a loss of SIG RETURN (sensor ground, which is not the same as chassis ground). Might want to pull PCM connector and look for VREF and SIG RETURN pins corroded, damaged. If VREF was damaged internally in the PCM a code would be set for that.
 

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Discussion Starter · #4 ·
Check engine codes

Well here is a list of some of the codes that are showing up:
P0453-Evaporative Emission Control System Pressure Sensor High Input
P0451-Evaporative Emission Control System Pressure Sensor Range/Performance
P0708-Transmission Range Sensor High Condition
P0121-Throttle position sensor range/ performance problem
P0123-Throttle position sensor switch a high input
P0118-Engine coolant temp sensor high input
P0143-Circuit Condition Heated Oxygen Sensor Bank
P0113-Intake air temp circuit high input
P0713-Transmission Fluid Temperature Sensor Circuit High Input
P1702-Transmission Range Sensor Circuit Intermittent
P1121-Throttle Position Sensor Inconsistent with Mass Air Flow Sensor
P1117-Engine Coolant Temperature Sensor Circuit Intermittent
P1112-Intake Air Temperature Sensor Intermittent
P0553-Power Steering Pressure Sensor Circuit High Input
P0193-Fuel Rail Pressure Sensor Circuit High Input
P1437-A/C Evaporator Air Temperature Circuit High
Also codes are coming up for the transmission fluid temperature.

I know that these are not all of the codes, but I didn't write the rest of them down. I know that a few of them were repetitive codes for the same sensors. I also have checked the pcm visually by removing the harness connector and none of the pins seem to have any corrosion or damage.
 

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Intermitent bad ground connection to PCM inputs.

I have schematic only to 2001 and there would be the "SIG RTN" is the Gry/Red wire to PCM. It goes "everywhere" - to almost all the sensors.
 

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There is a particular sensor that when shorted, will cause a 5 V reference failure for a bunch of other monitors. I've forgotten which thing it was, though...Iwant to say either TPS or IAC or maybe intake air temp sensor.
 

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What SoNic67 said.... virtually all those sensors are indicating voltage out of range on the high side. A loss of SIG RETURN will cause all of those codes. Check PCM connector as a first step.
 

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Discussion Starter · #8 ·
I re checked the connector yesterday by just pulling it off of the pcm and none of the pins show any signs or corrosion on them and they all seem to be intact. Is there a certain way that I should check for a good connection at the pcm other than doing this, or should I start looking for the problem elsewhere?
 

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Check from PCM connector SIG RETURN to the SIG RETURN at each of the sensors showing out of range codes with an ohm meter. Should be a few ohms max, like well under 10 ohms. There are big splices in the harness that can become intermittant, or the harness could have been pinched / worn thru somewhere.
 

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I dont think it is a PCM problem. If the PCM looses its internal 5V VREF, of VREF goes high (over the 5V) internally, it will set a VREF code, not a ton of sensor codes. In addition to possible intermittant in the SIG RETURN circuit to the PCM, if the VREF shorts to a 12V circuit in the harness, PCM will report all thiose sensors with overvolt input to PCM, but I THINK, PCM will also set a internal loss of VREF (VREF high) if this happens.
 

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Plus is less likely that two isolated wires to get their wires in contact. More likely that one will breake - the commun return (ground) from sensors. Like I said on the other page.
 
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