This is a new-to-me long neglected car, and had several chewed wires when I got it. I re-attached wires that I found chewed as best as I could: the TPS, #1 O2 sensor, and all spark plug wires. This car has an automatic trans, the flashing D4 light code is #10, "Coolant Temperature Sensor open or shorted." The check engine light codes are #6, "ECT-Water Temperature Sensor," and #10, "IAT-Intake Air Temperature Sensor."

To start the engine when cold it is easiest with a shot ot ether, then swiftly playing with the throttle pedal till it will run at about 2500-3000 rpm for a minute. Then I can let it settle down and idle on its own. Without ether, it takes a half dozen or more tries, and I have to catch it in the first half-second that it fires, and try to again keep it running by playing with the throttle. (When the engine is warm it starts quickly and easily)

Fuel pressure is reasonable. Injectors have been cleaned by me, Idle Air Control Valve seems to be fine, and so does the Fuel Pressure Regulator. The engine has lots of power once it gets past the initial starting difficulty, more than I would expect from a 2.2 four cylinder engine.

I have read statements and also seen videos, that claim that failing Intake Air Temperature sensors and Coolant Temperature sensors can be a cause of starting difficulties. Unplugging the IAT sensor and checking the resistance, it reads about 3000 ohms at about 30 degrees F. Removing it and checking resistance while holding it in front of a heater, makes the resistance slowly decrease. (much slower than I would expect) Checking voltage at the connector, while it is removed from the sensor, with Key On Engine Off, I get 5 volts at each of the two terminals.

As for the Coolant Temperature sensors it seems as though there are 3 or 4 of them. The one I have checked so far has a bright green connector and is located at the front of the engine, immediately before the attachment of the upper radiator hose. Unplugging the connector and checking the resistance, the sensor is an open circuit. Checking voltage on the connector while it is unplugged, Key On, Engine Off, the White/Green stripe wire reads 11 volts, and the Black wire reads 5 millivolts.

Here are my questions:
1) Does the IAT sensor sound like it is faulty, and are the voltage readings on the two wires connected to it proper, or improper?
2) The Coolant temperature sensor must be bad with an open circuit, but are the voltage readings on the 2 wires appropriate?
3) Someone please explain what the other two or three coolant sensors do. I have read/heard that the pencil thin one is for the dash guage, the one with the bright green connector on the thermostat housing is a switch to turn on the cooling fans, and I wonder what the one halfway between those two, with the olive drab connector does?

Thanks to anyone who will chime in with corrections and/or information on these questions and statements!

 

How did you repair the chewed wires on the harness?

When measuring voltage on a wire, the red meter lead should be on the wire you are testing, the black meter lead should be on ground (like the - battery post or the engine block).

The IAT sensor should have two wires (a red/yel and a grn/wht wire). The red/yel should have 5V to ground using a volt meter. The grn/wht wire goes back to the ECU, and I don't would have voltage from the ECU, but I'm not 100% sure on how the ECU circuit board. Measure voltage from grn/wht to ground to see what you get.

The 93 accord has 4 items dealing with coolant temp.

1. Temp Switch A is on the thermostat housing with a green connector. Switch closes when coolant reaches 200 °F and turns on the cooling fans when the engine is running.
2. Temp Swich B is near the upper radiator hose and also has a green connector. Switch closes when coolant reaches 223 °F and turns on just the radiator fan when the car is turned off. This is the switch you tested and is likely good. This switch will not cause the code 10.
3. ECT is under the distrubtor and has 2 wires in the connector. The ECU uses the signal from this sensor as the coolant temperature. This sensor or the wiring causes the code 10.
4. Engine coolant sending unit is also below the distributor and only has one wire going to it. This sensor only controls the gauge in the instrument cluster.

The voltage test is the same test as you do on the IAT. Yel/grn wire should have 5V, where the grn/wht wire shouldn't have voltage when using a good ground like before.

I'm using a 93 shop manual I found online a long time ago, but it covers non-US accords. The wire colors I listed could be wrong, but the voltage test will still work. One wire to each of those sensors should have 5V.

 

Thanks for your response, PAhonda! Wires to TPS were missing maybe 8 inches chewed off. I could not reach them to repair them, so I intercepted the three wires just before they reach the connector on the left fender. (I found the same color wires in the wire bunch) I cut them and, connected new wires, ran them to the TPS, and connected them with crimp connectors to the wire stubs still on the TPS. Later I saw a wiring diagram that seemed to show the red/x wire also connected to the TCU, so I also connected that new red/x wire back to the dangling abandoned original red/x wire. This was in case the intersection was somewhere in the harness that I could not see. And if it was not, then it should not matter, since I was able to cap off the end of the abandoned wire. Back probing and testing the TPS showed me that I had the appropriate voltages and ground on the three wires, and moving the throttle would smoothly raise and lower the voltage on the appropriate wire.

For the O2 sensor which was missing a couple inches of wire, I added a bit of wire and crimp connected them in place. After doing so, I saw a wiring diagram that showed one of the two heater wires to be positive, running to the ECU. Where I connected them I had no idea that there was any difference between the two black wires, so they may be switched, which I think (and hope) would not make any difference.

Spark plug secondary wires were just all replaced with a new set. I still see a wiring connector under the air intake rubber tube which has another connecter attached to it. The one connected one has two wires chewed down to the nub, and I have searched a few times and never figured out where they came from. I will take a picture of that and try to post it, when I work on the car later. (By the way, I entered descriptions of my vehicles in my profile, and they do not show up on this thread)

For the IAT sensor, I will double check. I was using the VOM with black lead to battery ground, and red wire to the connectors, as you suggest. I was very surprised to read 5 volts on both connector wires, as I think the ECU is supposed to supply a ground, and will run that test again.

Thanks for clearing up the coolant sensor question. I sounds as though the olive drab connector is the one I need to pull off and check. Are you saying that all of the coolant sensors should read 5 volts? If so, the switch B should not have 11 volts on one terminal, so I need to check that again also. Will post later with updated info.

 

Click on the triangle next to your username at the top of the site and select edit options. There is a checkbox to show your signature in your posts. That should fix the signature problem.

The O2 sensor heater circuit isn't directional, so you can switch the heater + and ground wires and it will work without issue.

The coolant temp switches are on a 12V circuit, so you are good on the green connectors.

The olive colored is on a 5V circuit.

I was hoping you said you tested the IAT sensor with the volt meter leads on the connector pins. Now that I know you were on ground, you still have an electrical problem for that sensor. You'll likely have to back-probe at the ECU for the grn/wht wire to measure voltage at the ECU to see what the ECU is seeing.

I'm not sure about the red/x wire you described. Since you have rodent damage to the wiring, I'll suggest you pull off the plastic covering for the wire harness in the areas of damage to find any other damage to the wiring.

It might be worthwhile to find a 93 accord at a u-pull-it yard and just replace the harness if the damage is extensive. Crimp connections are ok if done properly. Soldering and shrinkwrap is more permanent. I had to repair crimp connectors on my 95 that eventually failed that were done by the previous owner or maybe a body shop.

 

I checked both of the wires to the IAT sensor, they both have 5 volts. Actually one is a tiny bit less that 5, one a tiny bit more than 5, but basically 5v. It is the same story on the ECT Olive Drab connector, both terminals have 5 volts. (one a little over 5, one a little under) The ECT sensor shows about 4300 ohms resistance, while it is still in the cylinder head. And with all this pulling and testing, the 10 amp Meter fuse under dash has blown twice, so the CEL does not light. I will put everything back together, install a new fuse, and see if it blows again.

I have had the ECU and TCU out at different times to check for bloated or burned components or cracked solder joints. I wonder if there is a better way than I have experienced. It is so tightly wedged into it's place that it would be nearly impossible to find a wire and be able to probe it. Unless the right way is to pull out the wiring harness a foot or more in both directions, if that is even possible, in order to access everything for servicing or testing.

I took a picture of the connector I mentioned which has wires chewed to the nub. It has two wires, a blue/green and a blue/yellow.


The chewed end shows in this photo.

As for trying to find and install a replacement harness, I think it might be close to impossible to replace things without dismantling a great deal of the engine compartment, and maybe under the dash also. I wonder if it would work to cut the wires that are supposed to go to the ECU, cap them, and just run a new wire to ground for the IAT and ECT sensors, eliminating the ECU from the equation. Or is this just an unworkable silly idea?The only problem for this portion of the project is cold starting, since it runs so nicely once it gets going.

I also have an idea to pulse all 4 injectors before cranking a cold engine, some way to mometarily ground them out so they act like a shot of starting fluid. I'm not averse to trying some non-OEM methods to make this car start better.

Thanks for all your input and information!

 

You can't cut the wire back to the ECU, because the ECU uses the voltage change from the return wire to get the reading.

I'm not a fan of modifying wiring especially on the ECU-controlled fuel system. You risk other electrical issues with the ECU when something is grounded that shouldn't be. Working through and repairing the wiring should resolve the problem.

Can you post a picture of the connector from further out. I have no idea where you are at in the engine compartment, so I can't figure out what is nearby.

A fuse shouldn't blow from plugging/unplugging. Which fuse number is blowing in the picture below?

 

I'm not holding the connector in question, it is loose, down below that connector showing all the multi-colored wires. I'm holding the spark plug wires aside to show the area better.

The fuse that is blowing is #1, 10 amp, labled back up lights, meter lights, and in parentheses (turn signals), though turn signals work.

Tach does not work, CEL does not work, Transmission lever will not move out of Park, etc. Only red battery light shows up above speedometer when key is in on position. Engine will still start and run.

 

I have a non-US manual for the 93 accord and some things aren't matching up, so I'm confused.

What are the first 12 digits of the VIN? I want to make sure I'm looking at the correct manual. The VIN is on the driver's side of the windshield towards the bottom stamped on a metal plate you can see through the windshield glass. I just want to verify the year and trim information.

 

The complete VIN: 1HGCB7642PA171221. Thank you for taking all of the time and energy to assist me in tracking down and overcoming these problems! I'm sure it takes knowledge, determination, patience and skill to try to diagnose this car, multiplied by it not being in your phyical presence!

There is one more situation which I thought had been overcome, but might still be in the picture. When I originally had problems with the automatic transmission it would throw a TCU code 9, "Counter shaft or transmission speed pulse generator open or shorted." The car seemed to need more speed than appropriate before shifting into 3rd and 4th gears, and would not downshift to third when trying to pass someone. (It would downshift to 3rd if I used the shift lever, but not by mashing the accelerator pedal.) After I changed that pulse generator the trans would shift ok, but I would continue getting that code, despite trying multiple times to erase it. Last time I read the codes it was finally gone, but I recently realized that I had not driven the car after erasing the codes, and that might be the reason it had not thrown that code again.

 

Your VIN is for a 93 DX. Your challenge is to idenitfy and repair the wiring damage first, then address any other issues/failed components. I don't have an accurate wiring diagram/shop manual for the 90-93 accord. The manuals I accumulated through the years for the 4th gen accord are ok, but not comprehensive for wiring issues.

You are at the point where you need to decide if testing/repairing the wire harness is easier, or replacing the engine bay harness is "better". Better can mean easier, cheaper, or quicker and you have to make that call.

Harness repair will require a good shop manual with an accurate wiring diagram, so a month subcription from all-data or equivalent is needed. Ebay for the paper manual plus the electrical manual would be needed. Then you'll have to use a volt meter and test light to run through wiring from the ECU/TCU. It will be tedious, but certainly doable.

For replacing the engine bay harness, go to an oem parts site like hondapartsnow.com and enter your vehicle information. The drawing in there shows the cartoon version of the engine bay wire harness and where it ends to give you an idea of the connections to get it removed. Then you'll have to source the wire harness. I'm a fan of u-pull-it junkyards if you can find the same vehicle. Ebay is another source.

I'm not sure which route you prefer.