Author Topic: Honda Jazz 2003 1.4 - OBD error codes po638 and po100  (Read 1067 times)

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Honda Jazz 2003 1.4 - OBD error codes po638 and po100
« on: October 21, 2018, 06:10:22 PM »
Hi All :)

First time posting here, though I've frequently found this site a useful resource for fixing bits on my Jazz in the ~8 years I've had it. Hopefully someone here will be able to shed some light on an issue I'm currently experiencing and have had difficulty debugging.

Got home last night and when I stopped to pull in to the drive, noticed check engine light had come on. At the same moment, whilst stationary, the revs started jumping up and down from ~500 - 1500 rhythmically every ~1 second.

I hooked up my ODB scanner this morning and got two error codes registered: po638 ("Throttle Actuator Control Range/Performance") and po100 ("Mass of Volume Air flow - circuit malfunction""). I tested the absolute throttle sensor position at idle and fully depressed and saw it was fairly consistent with a low of ~12% and a high ~86.3%. I also noticed however, that occasionally it appeared to jump from ~12% to 16% without any depression. When it did this, it fluctuated between 12-16 erratically, though I couldn't reliably reproduce the effect consistently.

After doing some research on the issues and checking there was nothing obviously loose/damaged in the engine bay, I found the check engine light had turned off. I took it for a quick test drive and found that the acceleration seemed erratic, though only marginally. It seemed to occasionally "jump" a little, though this didn't seem major and the light didn't re-appear. When I stopped at a junction close to home however, the light re-appeared, and the acceleration all but disappeared. I was only able to get up to ~15mph and had to crawl the last few hundred meters home (I believe this might be the "limp home mode" kicking in?).

I've found numerous threads discussing the po638 issue (most notably this one https://honda-tech.com/forums/honda-fit-73/honda-jazz-fit-2005-p0638-p0122-3186613/), and it seems like a lot of the time, the cause is a faulty wire in the connector. Unfortunately, I was unable to work out which connector this cable was and haven't been ale to confirm if this is the issue or not. It also seems the issue could apparently lie with the throttle position sensor or some other component of the throttle assembly. Given that I could only find the sensor bundled with the whole assembly, and not cheaper than ~£300, I'm really reticent to spend money and time repairing this without knowing it is definitely the root cause of the issue (hence reaching out here).

As for the po100 issue, that seems to be thin on the ground, and and I've not had much luck at all working out where to start with that. Seems like it might be worth removing and checking the MAF sensor for damage/dirt, but again I've had no joy working out which specific component this is or best approach to debugging it further.

As for the combination of the two error codes, I haven't had any joy at all! :( Maybe this is an uncommon combination of errors...

I've got a Haynes manual on the way to hopefully help me locate the specific TPS connector and MAF sensor, but given teh level of ambiguity in the issue I'm not that optimistic.

If anyone has any similar experience or useful related information I'd greatly appreciate the help :)

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