Chevygirl93

I will have to see exactly

Gumby22

Sorry for the delay in posting these - the past couple days have been hectic.

All the power and ground feeds for the PCM can be verified with a test light or a meter - my recommendation is to start with a test light (hooked to battery positive or negative respective to the feed you’re testing), then if it’s glowing dimly, use a meter to verify.

If using a test light, remove the connector from the PCM - if using a meter, you can remove the connector or back probe it using a sewing needle or safety pin (if you don’t have probes for the meter).

You should also disable the starter - some of the switch feeds should have power when the key is in the on or crank position, so disabling the starter will prevent unnecessary drain on the battery.

C1 (Blue)
- pin 4, pink wire, from ENG 1 fuse (underhood), hot in run and start

C2 (Red) - no power or ground feeds

C3 (Clear or Gray)
- pin 12, gray wire, 5v reference to engine controls from PCM (check with meter while back probing connector, key on engine off - if it’s less than 4.5 volts and all the other power/ground feeds are good, the PCM is bad)
- pins 17 & 18, black/white wires, grounds to rear of right cylinder head
- pin 21, orange wire, direct battery feed via ECM b fuse
- pin 27, gray wire, 5v reference to engine controls from PCM

C4 (Black)
- pin 13, brown wire, from brake fuse (cabin), hot in run
- pin 18, pink wire, from ECM 1 fuse (underhood), hot in run and start

Note that the underhood fuses ENG 1 and ECM 1 both get power from the same circuit from the ignition switch. If you find that there’s a significant difference between the power feed in C1 vs the power feeds in C4, it could be a problem with the underhood fuse box or with the splices located in the harness. However if you find that all 3 power feeds read the same but are substantially lower than battery voltage, trace the circuit between the underhood fuse box and the ignition switch to isolate the open or high resistance and repair as needed.

Chevygirl93

Okay, here's what I found out using a test light and a volt meter. All pins on each connector that has power does. Everything seems to test out right. So I went ahead and ordered a new PCM. Is there any way to test the PCM while it is out just out of curiosity.

Gumby22

The rule for testing any control module is “test the inputs and the outputs.” The inputs are power and ground feeds and anything the PCM needs to function, such as a crank signal. The outputs would be anything the PCM controls, in this case, the spark output.

On connector 3, back probe pin 9, white wire, and watch for the voltage to peak around 4 volts AC while cranking - this is the signal the PCM sends to the ICM to command spark. If it’s there, check for an open or high resistance between pin 9 and pin B at the ICM (or monitor for 4 volts AC at the ICM).

If it’s not there, first verify the crank signal at the PCM by back probing C1, pin 31, yellow wire and looking for about 10 volts AC while cranking. If it’s there, consider the PCM bad. If it’s not there, troubleshooting the crank sensor and related wiring is the next step before PCM replacement.

RJ Rowles

Check ground under dash from ignition could be loose or broke

Techtodd

1)You have a DUI distributor? Which part number ?
2) you must have cam and crank signal for spark.
The crank gap reference comes around every TDC (exhaust and compression). The cam sensor gap reference come around only on #1 TDC compression(when its time to spark). The computer requires the starting point from the cam sensor before it knows where the crank is.
i dont know why someone told you the cam sensor isnt needed for spark, and i havnt read in your thread where you've scrutinized the cam sensor.
3)you may have a compatibility conflict with the sensor in your aftermarket distrib, or its non functional, or you have a distributor with no cam sensor, which you must have for the tbi to function.
Sorry for your troubles, hope this gives you some help.

Chris94

Carefully remove any covers you can and look inside for leaking/blown capacitors. I just did a bunch of troubleshooting to figure out why my '97 Corolla wouldn't stay running more than ~1min and everything was passing inspection, even the ECM. I yanked it out and found leaking capacitors and damage to the circuit board. Normally you'd want to use an anti-static wrist strap when working on circuits. Picture of my Corolla's ECM for reference.