I have a p0112 code ( Intake Air Temperature Sensor 1 Circuit Low) on my ob2 scanner and a p0135 ( O2 Sensor Heater Circuit Bank 1 Sensor 1). I haven't changed my IAT sensor because I'm confused on the location of it and I tried changing my O2 sensor with multiple other sensors from Civics and other Accords from Pick n Pull (Junkyard) and the p0135 doesn't go away. Someone Help

 

The IAT is on the upper part of the intake manifold towards the driver's side. The wire colors to the connector should be red/blk and grn/blk.

The P0135 is for the heater circuit on the upstream O2 sensor. Your car has two O2 sensors. The upstream is on the exhaust manifold in the engine bay and the downstream is on or just past the catalytic converter. Have you replaced the one on the bottom of the exhaust manifold?

 

I changed the IAT sensor and cleared the code and the code popped up again right away. I also replaced both of my O2 sensors and the same code popped up.

 

When a check engine code is set, the root cause can be the sensor, the wiring/electrical connections, or the ECU. Most of the time, replacing the sensor fixes the problem. In your case, the sensors didn't resolve the issue. Made a mistake on my previous post and the IAT wire colors are red/YEL and grn/blk. Verify the wire colors to that sensor are correct.

Do you have a scanner that can read live data? Also do you have a volt meter? The next step would be to see what the IAT temperature reading is at the ECU and a scanner that reads live data would make quick work of this. The grn/blk wire should have voltage. I'm pretty sure it will be 5V, but it could be 12V. Honda's troubleshooting diagnostic is lacking in my opinion.

Similar setup for the O2 sensor heater circuit. The upstream O2 sensor has 4 wires. Two wires are the power and ground for the heater in the O2 sensor. These two wires should be opposite of the locking tab in the electrical connector. Looks like the wire colors are blk/wht and blk/yel. Before you do any testing, please verify the wire colors. The wire colors on the sensor side of the harness may have the same color. Using a volt meter to test for power on one of the wires (not sure which one is the power) is safe test. Use the - battery post as the gorund for your volt meter. If you use a 12V test light, you need to be 100% sure you are on the correct wires, or the test could damage the PCM/ECU.

 

I looked the data stream on my IAT sensor and noticed it was stuck on 215C. The wire colors for my IAT sensor are green and black with silver dots going along them. My green IAT sensor had 14V at the connector on the harness side. And I also checked both of my O2 Sensors and the yellow and black wire had 14V on both of them. I was using a multimeter for these tests.

 

The shop manual isn't usually wrong on wire colors, but it is possible. Look at the connector for the IAT and see if any sensors nearby where the current IAT connector can reach. It is possible connectors got switched. The 94-97 accords had a couple connectors, but I'm not sure on the 98-02.

For the O2 sensor, I'd get a 12V test light and connect to the yel/blk and a good ground (any bare metal on the engine block). You have 12+ volts, but you want to verify the wire can provide enough current.