Does the PCM provide the on/off signal to the ECM on 94 mercury tracer 1.8L engine. If so what color wire do I test to verify the signal output from the PCM. Schematicv would be great.

DTC P1637

The powertrain control module (PCM) / engine control module (ECM) uses the charge indicator control circuit, and the generator 2 turn on signal circuit on diesels with dual generators, to control the generator(s). A high side driver within the PCM/ECM allows the PCM/ECM to turn the generator ON and OFF. When generator operation is desired, the PCM/ECM sends a 10-11 volts-volt signal to the voltage regulator via the generator turn on signal circuit. This causes the voltage regulator to begin controlling the generator field circuit. Once the generator is enabled by the PCM/ECM, the voltage regulator controls generator output independently of the PCM/ECM. Under certain operating conditions, the PCM/ECM can turn OFF the generator by turning OFF the voltage on the charge indicator control circuit. The PCM/ECM has fault detection circuitry which monitors the state of the charge indicator control circuit. If the fault detection circuit senses a voltage other than what is expected, the charge indicator will turn ON and this DTC will set. The voltage regulator also contains fault detection circuitry. If the regulator detects a problem, the regulator will ground the charge indicator control circuit, pulling the voltage low. This also causes the charge indicator to turn ON and the PCM/ECM to set the DTC.

What engine is in your truck ?

DTC P1638

The powertrain control module (PCM) uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator. The generator field duty cycle signal circuit connects to the high side of the field winding in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field winding ON and OFF. The PCM uses the PWM signal input to determine the generator load on the engine. This allows the PCM to adjust the idle speed to compensate for high electrical loads.
The PCM monitors the state of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5-100 percent. The PCM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the PCM detects an out of range PWM signal, DTC P1638 will set. When the DTC sets, the PCM will send a class 2 serial data message to the IPC to illuminate the charge indicator.

Do you know how to test starter electrical circuit using voltage drop ? Test the battery cable to the starter . Plus ,knowing how the starter system works helps , it's not just a wire from the ignition switch to the S terminal on the starter solenoid . Turning the key to start a low voltage input to the BCM , indicates start is requested . The BCM sends a start request to the PCM / ECM - engine computer . The engine computer will energize the crank / start relay sending battery voltage to the S terminal on the starter solenoid spinning the engine over .
https://www.youtube.com/watch?v=XhRPLgH6uZg&t=2s
Do you know what a wiring diagram is ? How to use a DVOM - digital volt ohmmeter to test electrical circuits . Free wiring diagrams here http://www.bbbind.com/free-tsb/ Enter vehicle info. Year , make , model an engine . Under system click on engine then under subsystem click on starting . Click the search button then the blue link.

Circuit Description
Moving the ignition switch to the START position signals the body control module (BCM) through discrete inputs from the ignition transducer that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the engine control module (ECM)/powertrain control module (PCM) requesting engine start. The ECM/PCM receives a 12-volt signal from the park/neutral position (PNP) switch or clutch pedal start switch notifying that it is safe to start the engine. There is a splice on this circuit in the fuse block-underhood that supplies power for the starter relay coil. The starter relay coil control circuit is then grounded by the ECM/PCM closing the switch in the starter relay suppling 12 volts to the S-terminal of the starter. Ground is supplied through the engine block.

What ECM code ? What is everything else that is working ? Headlamps , inside lighting , radio etc... When you turn the key on do the instrument cluster warning lights come on then off a few seconds later ? Anti-theft (security light ) On ? Flashing ? Do you know what all is involved ,or happens when you turn the key to start ?
Circuit Description (ECM/PCM Controlled)
Moving the ignition switch to the START position sends a 12-volt signal to the engine control module (ECM)/powertrain control module (PCM) Crank Request circuit. The ECM/PCM verifies that the transmission is in the PARK or NEUTRAL position. With the transmission in Park, voltage flows through the Park/Neutral position switch and feeds the starter relay coil. The PCM then grounds the control circuit of the starter relay. When the starter relay is energized it allows battery positive voltage to the starter solenoid S terminal. On some vehicles the starter will continue to crank the engine with the key released until it starts or the crank command has timed out to prevent excessive heat build up in the starter circuitry or the ECM/PCM receives an engine run flag.
Circuit Description (BCM Controlled)
Moving the ignition to the START position signals the body control module (BCM) that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the powertrain control module (PCM) requesting engine start. The BCM also energizes the RUN/CRANK RELAY. When the RUN/CRANK RELAY switch side closes, and the vehicle is in Park or Neutral or with the clutch is fully depressed, if equipped, supplies voltage to the starter relay coil. The PCM verifies the transmission is in Park or Neutral and the clutch is fully depressed, if equipped. The PCM will then ground the control circuit of the starter relay, closing the switch supplying voltage to the starter solenoid. On some vehicles the starter will continue to crank the engine with the key released until it starts of the crank command has timed out to prevent excessive heat build up in the starter circuitry or the PCM receives an engine run flag.


Verify that no starter relay, immobilizer, or automatic transmission DTCs are set that would cause the PCM to disable starting.
? If the specified DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
Ignition ON, observe the scan tool PCM Ignition 1 Signal parameter with a scan tool. The reading should be greater than 10.0 Volts.
? If less than the specified value, test the ETC, PCM 1, and PCM B fuses, the RUN/CRNK relay, and the PCM ignition voltage circuits for an open/high resistance. If the circuits test normal, replace the PCM.
Ignition OFF, remove the START relay.
Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
? If the test lamp does not illuminate, test the START fuse and the B+ circuit for an open/high resistance.
Ignition ON, transmission in Park or clutch pedal pressed, verify that a test lamp illuminates between the PNP/clutch start switch signal circuit terminal 86 and ground.
? If the test lamp does not illuminate, test the IGN fuse, RUN/CRANK relay, PNP/clutch switch ignition voltage circuit, and the signal circuit for a short to ground or an open/high resistance. If the circuits test normal, test or replace the PNP switch or the clutch start switch.
Connect a test lamp between the park/neutral signal circuit terminal 86 and the relay coil control circuit terminal 85.
Ignition ON, transmission in Park, or clutch pedal pressed, turn the ignition switch between the START and RUN positions. The test lamp should turn ON and OFF when changing between the commanded states.
? If the test lamp is always ON, test the relay control circuit for a short to ground. If the circuit tests normal, replace the PCM.
? If the test lamp is always OFF, test the relay control circuit for a short to voltage or an open/high resistance. Test the PNP/clutch start switch signal circuit for an open/high resistance. If the circuits test normal, replace the PCM.
Install the START relay.
Connect a test lamp between the starter solenoid terminal and ground.

Crank sensor or coil. Rare instances, could be the ECM or wiring.

Will a scan tool communicate with it or on the screen does it say NO COMM ! That's how you test a PCM/ECM . If no comm ,check power an ground's ,that's it .
Why were you messing with the crank sensor ? If the fuel pump primes for two seconds there is nothing wrong with it . When cranking the engine the PCM/ECM will only energize the fuel pump if it see's an input from the crank sensor ! You will not see 12 volts on the crank sensor signal return wire ! Crankshaft Position (CKP) Sensor
The CKP sensor is a three wire sensor based on the magneto resistive principle. A magneto resistive sensor uses two magnetic pickups between a permanent magnet. As an element such as a reluctor wheel passes the magnets the resulting change in the magnetic field is used by the sensor electronics to produce a digital output pulse. The PCM supplies a 12-volt, low reference, and signal circuit to the CKP sensor. The sensor returns a digital ON/OFF pulse 3 times per crankshaft revolution for the V6 engine, 4 times for the V8 engine. The CKP sensor reads the crankshaft mounted reluctor wheel to identify pairs of cylinders at top dead center (TDC).

Duplicated question, already answered

For each code there is a diagnostic testing procedure . Without doing the testing we would only be guessing as to the problem . Sounds like you know next to nothing about automobile engine management systems . Your best bet ,take it to a qualified repair shop .
P0443 - EVAP Control System Canister Purge Valve Circuit Malfunction The PCM monitors the state of the EVAP canister purge valve circuit output driver. The test fails when the signal moves outside the minimum or maximum limit for the commanded state.

• VPWR circuit open
• EVAP canister purge valve circuit shorted to GND
• Damaged EVAP canister purge valve
• EVAP canister purge valve circuit open
• EVAP canister purge valve circuit shorted to VPWR
• Damaged PCM

To verify normal function, monitor the EVAP canister purge valve signal PID EVAPPDC (or EVMV for electronic valve) and the signal voltage (PCM control side). With the valve closed, EVAPPDC will indicate 0 percent duty cycle (0 mA for EVMV) and the voltage approximately equal to battery voltage. When the valve is commanded fully open, EVAPPDC will indicate 100 percent duty cycle (1000mA for EVMV) and a voltage drop of 3 volts minimum is normal. Output test mode may be used to switch output ON/OFF to verify function.
P0135 - HO2S Sensor Circuit Malfunction (HO2S-11) During testing the HO2S Heaters are checked for opens/shorts and excessive current draw. The test fails when current draw exceeds a calibrated limit and/or an open or short is detected.

• Short to VPWR in harness or HO2S.
• Water in harness connector.
• Open VPWR circuit.
• Open GND circuit.
• Low battery voltage.
• Corrosion or poor mating terminals and wiring
• Damaged HO2S heater.
• Damaged PCM.

• Wiring.
• Damaged HO2S heater.
• Damaged PCM.

P0155 - HO2S Sensor Circuit Malfunction (HO2S-21) See DTC P0135
P0755 * SSB, wiring, PCM SSB solenoid circuit failure SSB circuit fails to provide voltage drop across solenoid. Circuit open or shorted or PCM driver failure during on-board diagnostic. Incorrect gear selection depending on condition mode and manual lever position. See Solenoid On/Off Chart. Go To Pinpoint Test A .
P1747 * EPC, wiring, PCM EPC solenoid circuit failure, shorted circuit or output driver Voltage through EPC solenoid is checked. An error will be noted if tolerance is exceeded. Short circuit causes minimum EPC pressure (minimum capacity) and limits engine torque (alternate firm). Go To Pinpoint Test D .
P1401 - DPF EGR Sensor Circuit High Voltage Detected The EGR monitor checks the DPF EGR sensor signal to the PCM for high voltage. The test fails when the average voltage to the PCM goes to a voltage greater than the maximum calibrated value.

• DPF EGR circuit open
• VREF short to PWR
• Damaged DPF EGR sensor
• DPFEGR circuit short to PWR
• SIG RTN circuit open
• Damaged PCM

A DPF EGR PID reading greater than 4.5 volts with the key ON and engine OFF or running, indicates a hard fault.
P1451 - EVAP Control System Canister Vent Solenoid Circuit Malfunction Monitors the canister vent (CV) solenoid circuit for an electrical failure. The test fails when the signal moves outside the minimum or maximum allowable calibrated parameters for a specified canister vent duty cycle by PCM command.

• VPWR circuit open
• CV solenoid circuit shorted to PWR GND or CHASSIS GND
• Damaged CV solenoid
• CV solenoid circuit open
• CV solenoid circuit shorted to VPWR
• Damaged PCM

To verify normal function, monitor the EVAP canister vent solenoid signal PID EVAPCV and the signal voltage (PCM control side). With the valve open, EVAPCV will indicate 0 percent duty cycle and the voltage approximately equal to battery voltage. When the valve is commanded fully closed, EVAPCV will indicate 100% duty cycle and a voltage drop of 4 volts minimum is normal. Output test mode may be used to switch output ON/OFF to verify function.
Look's like you have multiple problems an to say what the problem could be would be guessing . Your best bet ,take it to a qualified repair shop .

ECM (Engine Control Module) is the old name to the new PCM
(Powertrain Control Module) denomination; this unit performs many functions on your car. The module accepts information from various engine sensors and computes the required fuel flow rate necessary to maintain the correct amount of air/fuel ratio throughout the entire engine operational range.

Based on the information that is received and programmed into the PCM's memory, the PCM generates output signals to control relays, actuators and solenoids.

The module is mounted under the hood on the firewall. On 493-94 models, it is mounted low on the firewall, near the left-hand fender (drivers side). On 495-99 models, it is mounted high on the firewall offset to the right-hand side of center.



Exploded view of the firewall PCM mounting for 493-94 models




Exploded view of the firewall PCM mounting for 495-99 models

1. Disconnect the negative battery cable.
2. Disengage the wiring harness connector from the PCM by loosening the connector retaining bolt, then pulling the connector from the module.
3. Remove the two nuts and the PCM cover.
4. Remove the PCM from the bracket by pulling the unit outward.
   

To install:

1. Install the PCM in the mounting bracket.
2. Install the PCM cover and tighten the two nuts.
3. Attach the wiring harness connector to the module, then tighten the connector retaining bolt.
4. Connect the negative battery cable.

Hope helps (remember comment and rated this).

I don't believe it has an IAT, (Intake Temperature Sensor). Heres what it has. Hope this helps. Cobra..
Electronic Engine Controls Printable View (63 KB) The electronic engine controls consist of the following:

• powertrain control module (PCM)
• throttle position (TP) sensor
• engine coolant temperature (ECT) sensor
• camshaft position (CMP) sensor
• crankshaft position (CKP) sensor
• mass air flow (MAF) sensor
• heated oxygen sensor (HO2S)
• knock sensor (KS)

The PCM carries out the following functions:

• accepts input from various engine sensors to compute the fuel flow rate necessary to maintain a prescribed air/fuel ratio throughout the entire engine operational range.
• outputs a command to the fuel injectors to meter the appropriate quantity of fuel.

The TP sensor:

• sends the PCM a signal indicating the throttle plate angle.
• is the main input to the PCM from the driver.

The ECT sensor:

• sends the PCM a signal indicating engine temperature.
• voltage decreases as coolant temperature increases.

The CMP sensor:

• sends the PCM a signal indicating camshaft position used for fuel synchronization.

The CKP sensor:

• sends the PCM a signal indicating crankshaft position.
• is essential for calculating spark timing.

The MAF sensor:

• uses a hot wire sensing element to measure the amount of air entering the engine. Air passing over the hot wire causes it to cool.

The front HO2S:

• creates a voltage signal dependent on exhaust oxygen content.
• provides feedback information to the PCM used to calculate fuel delivery.

The rear HO2S:

• monitors oxygen content after it flows through the catalytic converter.
• provides a voltage to the PCM used to calculate catalytic converter integrity.

The KS:

• is used to detect engine detonation.
• sends a voltage signal to the PCM.
• is able to provide a signal which retards the ignition timing, as necessary.