Ok355

I have a 1999 Civic GX (compressed natural gas powered engine), 30k. Automatic trans. All Stock. New battery.

-CEL is on.
-The engine idles / revs high & low constantly. When I drive it stays at a higher than normal rev, but at idle it is erratic.
-The speedometer and mileage counter do not move when driving. The rest of the instrument cluster works, including the fuel and temp gauges.

I have encountered these codes:

P1298 Injector Driver Module Failure
P0135 H025 Heater Circuit, Bank 1 Sensor 1
P0141 H025 Heater Circuit, Bank 1 Sensor 2

I saw in a FAQ that the P1298 was listed as something else, Electric Load Detector (ELD) Circuit High Voltage. However, I am confident that mine is related to the Injector Driver Module Failure, but I am not sure how to rule out CHV.

1. Do these codes work together, one triggering the next?
2. Have you ever encountered these codes all at the same time?
3. In light of the P1298 fault, my greatest concern is the cost of replacing the Injector Driver Module, any idea how much this part costs? Is there any way to test the questionable part?

Any help would be great. Thanks.

Newfiedan

well first off do a tune up if you have never done one, meaning fuel filter, air filter, plugs, wires, cap/rotor and plugs, make sure that both battery terminals & connectors are clean and tight.

P1298 Electrical Load Detector Circuit High Input, this usually indicates a crappy engine ground, clean it and reattach it or for a quick test attach a jumper cable from the negative terminal of the battery to the engine see if it clears up the code if it does then the grounds need to be replaced. It can also mean that the charge wire is corroded and not doing its job, placing an unnecessary load on the alternator.
Next check fuse 15 see if it is blown in the interior fuse panel. For that matter check all the fuses it sounds like you have blown one that controls the vehicle speed sensor.

Ok355

Fuse #15 (7.5amp) was blown. I looked at the engine wiring harness near the intake manifold bracket and could not find any damaged wires, however considering the tight location I do intend to look at this again much more thoroughly after finding that fuse #15 was blown. I can't see how else fuse #15 would blow unless a wire is damaged on the harness.

I also pulled an ELD out of my 99 Civic Si and put it in my 99 Civic GX. The part fit and plugged-in, however I am not sure if they are setup for different voltage parameters. Any idea if all 99 Civic ELD's are the same?

Presently it is still idling high and then low. When you start the engine it idles normal for about 2 mins, then the check engine light comes on and the fluctuating idle begins... It appears to be revving an additional 1000rpms over the normal idle range and then dropping to approx 500rpm's. The latter is causing the automatic transmission to shift strange as well.

My Civic recently underwent a full service, including a new battery. The car only has 30k with no mods, so it has been well cared for. I looked at all the grounds I could find, but I do plan to go back over them and clean them with sandpaper. Is there a diagram that shows where all of the ground wires are at just in case I missed one?

On Saturday I am going to try to pull the ELD & the 02 Sensors out of another low mileage 99 Civic GX. I will post an update after the swap.

Ok355

Here is the latest. Today I checked fuse #15 again and it was blown for a second time. I closely and thoroughly checked the wires by the intake manifold bracket, they all look good. However, I am certain I have found what is blowing fuse #15... I found 4 burned wires which connect to the downstream oxygen sensor. I unplugged the downstream oxygen sensor, replaced fuse #15 for a 3rd time and started the engine, then checked the fuse, it was still good. The engine was idling correctly so I drove it around the block for 5 minutes with no problems, after 7 minutes the engine idle started to rise and fall again. This time around, I suspect the latter is due to me disconnecting the downstream oxygen sensor (please correct me if that assumption sounds wrong). I returned to my house, turned the engine off and decided to plug the downstream oxygen sensor connector back into the engine wiring harness. As soon as I turned the key to position two, fuse #15 blew again. ....I did this to triple check that this was the cause for the fuse failure.

One thing I am certain about is that the 4 exposed wires were burned, as I found them laying across the exhaust heat shield. I intend to remove the oxygen sensor, cut the 4 wires, re-solder and seal them, then I will plug the sensor back in and see what happens to fuse #15.

As you know, there are two oxygen sensors, if the lower one of the two is not working and/or disconnected will it cause the engine to idle erratically?

Thanks

MelJ

The O2 post CAT just monitors the catalytic converter's efficiency. If that sensor has a similar reading to the one pre cat, then it means the CAT isn't working properly.

Newfiedan

if fuse 15 keeps blowing then you have a short to ground issue there somewhere and need to look for it. It may not be obvious right away so check over the 02 wiring very thoroughly, it may even be the sensor itself that has gone bad I have heard of that happening to a few civics over the years i think the worst one I found was one that had the 02 sensor tip totally gone causing a short. That may also be the source of your wonky idle, start eliminating the electrical problems and get yourself a auto ranging digital multimeter to accurately measure resistance and the like, its a great tool and they do not need to be expensive.

Ok355

New Problem. My OBDII is not working.

I've spent 3 weeks going over everything I was advised to look for, but just couldn't solve the bad idle. I decided to take my Civic to my trusted mechanic whom my family has come to trust over the past 20 years. He tried to run his expensive scan tool on my Civic and could not get any reading at all, as if the scan tool was not working. So next I drove the car to O'reilly's (an autoparts store) to have them scan it for codes. They could not get their scan tool to work either. Called my Honda dealer and they said they can't help me if they can't pull up any trouble codes.

Even though the idle would rise and fall 1000 rpm's while in park, I could still drive it and being in gear kept the idle steady. However, I decided to drive my Civic from the mechanic to my house and on the way, the idle went from odd to a lot worse. Now the idle hunts very erratically while in park, and when driving it nearly stalls out and stumbles.

In my earlier and original post a scan tool was working and getting codes. Now a month later scan tools can not pull any codes from the OBDII system.

What could be causing the OBDII not to work?

gearbox

iTrader: (95)

usually the ecu is bad if code readers do not work anymore. possibly caused by bad alternator thats not grounded or overcharging (producing more than 14.5v at warm idle).

Ok355

Thanks gearbox. I was afraid the ecu was going bad. I got lucky though.

OBD2 problem has been found...

7.5A fuse in slot 43 under the hood was missing, this fuse protects the circuits for the ceiling and trunk lights, and oddly enough also includes the OBD2.

Ok355

Problem solved.

After I replaced the bad 02 sensor that cleared the codes at the heading of this post P1298, P0135, P0141. The engine was still idling terribly, even worse than before, so I ran another scan and found these 2 codes: P0505 Idle Air Control System Fault & P1509 Idle Air Control Valve Circuit Failure.

I decided to replace the IACV with an OEM one for $155 and sure enough it fixed the problem instantly! No fault codes, no CEL. The engine runs great and idles just as it should.

Thanks to everyone who helped me.

1999 Civic GX (compressed natural gas powered engine).

Dogstns

I got the exact issue here thanks for updating this post even though it's old. You are a legend man