2008 Saturn Astra XR Code C0642

[Dr Gizmo]

I purchased this vehicle 2 weeks ago, 240,000 km . It needed a caliper and rotor replaced immediately but beside that, it is in pristine condition. Last weekend I washed the engine compartment, sparing as much water as possible. On startup now, it runs fro about 4 minutes, sputters, idle speed freezes at 1500 rpm, the speedo needle bounces around erratically and it gives me a code C0642. It is non specific and suggests grounding, low voltage etc. I spent 3 hours testing and cleaning all visible sockets and grounds. Every groung circuit I could see was cleaned with a wire wheel and when re-assembled , a star washer was placed to assure continuity. I'm frustrated and hioping someone can open another path to resolve this issue

[AstraFasta]

I don't know what that code is for. Chevy has this engine z18xer in a few popular small cars so those forums might be worth searching.

EDIT - Astra throws odd codes if voltage is low so check what voltage battery and alternator are running and with car off. Bad battery and/or alternator would be typical causes of odd voltage

First step is to reset computer by disconnecting the battery for a few hours.

But the underhood electrical box next to the battery does not seal properly and gets wet so that would be a quick stop for grounding issues. That is a rectangular black box on the right side of the battery. The clips pop off easily, the o-ring is lousy, water might enter from below where wires enter. This is a fix with photos:

https://www.vauxhallownersnetwork.co...fira-b.371985/

You can search my posts for some of the popular grounds for cleaning on the Astra. That could be conicidence with washing but frankly seems unlikely. I cleaned the grounds under the battery, under the UEC, at alternator, at engine, and all battery terminals/clamps. You could also run simple voltage drop tests with a DMM.

Some of the Astra wires, wire tape, black wire sleves are suspect so check for worn wires that might have been slightly moved during your cleaning. There is one black wire sleve on my Astra that wore out and required wire repair at the front/left/top of valve cover (those wires go to the MAF, and cam ACTUATORS I think but can't remember).

Unlikely ideas:

Try removing, drying and cleaning key connectors under the hood (including at UEC, MAF, cam solenoids, coilpack, etc.)

You might check the spark plug holes did not fill with water that just requires removing the plastic rectangle and coil pack from the engine and checking with a flashlight. Never heard of that problem with the Astra but easy check.

The alternator would be sensitive to pressure washing so that could be a problem. Never heard of that problem with the Astra but easy check.

[Dr Gizmo]

Thank you for your input, it was extremely helpful. I have a Chilton manual on order as Part Source, NAPA or Canadian Tire here in Ontario doesn't stock or order them in, I will keep the forum updated.

[AstraFasta]

I didn't know there was a Chilton's manual.

The UK Haynes Vauxhall Astra manual is popular here and I think it is somewhat helpful. I had to import it from Europe. It is a bit too general but has some good pictures and text so I usually combine Haynes with forum posts and internet searches.

Your local library might have a professional subscription service to one of the pro online manuals. Those are awesome but in my area I have to be physically at the library to see it.

[Astra08]

The 'C' indicates a chassis code, and the '0' is generic. The '6' points to a computer related item and the last two are the fault.

I'll check my Alldata subscription to see is there is anything specific.

[Dr Gizmo]

That would be really appreciated.

[Dr Gizmo]

I stand corrected, it is a Haynes manual I have ordered. Just hoping for anything very few visuals of anything technical or mechanical on the net

[Dr Gizmo]

Just an update. I have spent approximately 16 hours under the hood of my 2008 Saturn Astra sanding, filing and grinding every grounding point I can find and still get this nuisance C0642 code. Just to re-cap, starts fine and idles for about 3-4 minutes, then sputters and goes into limp mode, speedo needle bounces around for 30 seconds, then it stalls out. Only code that ever comes up is C0642 but I have searched and can not get a specific cause thus resolution. Any input would be greatly appreciated. If I were to take it to a garage, would there OBD equipment diagnose the exact cause of this issue?

[eric08]

If there is a shop you trust, that is an option. A high end scanner will be able to amass a large amount of live data and might be able to spot the true culprit. The trick is finding a shop that really knows what they're doing. There are too many that are glorified parts changers.

I had similar symptoms once on an entirely different platform, gauges jumping all over, poor running, and it turned out to be a bad voltage regulator(new alternator cured all). I was hoping you'd luck out with something similar but I assume you've checked your voltage drops by now and ruled that out.

[AstraFasta]

Most of tips I provided above are popular solutions for the Astra (I don't think I read about water submerging spark plugs however). A few other ideas.

On ocassion, computer boards need to be replaced and reprogrammed with Tech2 but that is not so common. I've seen a few dozen posts in Europe for this.

Are you running a stock dry airfilter with stock airbox? Oiled air filters regularly kill MAFs and cause drivability issues on the z18xer. Popular problem.

Crazy idle issues are often result of a bad IAC valve, which can fail haphazardly and be difficult to diagnose. I don't have the Astra manual or car with me so don't know if the z18xer has an IAC valve or if that is controlled by the computer. On other Astra engines fixes included replacing throttle body gasket or throttlebody.

Inside the car, the drive by wire potentiometer fails on ocassion so needs cleaning but that redundant system should throw a code, so I wouldn't expect that to be the issue.

Maybe research failing MAF issues also. Low probability as that usually throws a code. Clean it with MAF sensor cleaner and test.

For the wonky spedometer, one suggestion in UK boards was the wheel speed sensors. But I wouldn't go down that path now since you have other issues with electrics/power/computers which might be related.

[Dr Gizmo]

Wow, thank you for all the great suggestions. My Haynes manual finally arrived today from Great Britain, as there isn't 1 available for the North American Saturn Astra. I am aware I have issues with 1 or both of the ABS speed sensors but wouldn't figure they would cause the engine running/not running issues. I do have a friend from high school who owns a garage. He is intrigued with the issue and luckily his shop is within the 3-4 minute threshold that the engine will operate normally for. I dropped it off this morning. Will keep the forum updated.

[AstraFasta]

Originally Posted by Dr Gizmo

I am aware I have issues with 1 or both of the ABS speed sensors but wouldn't figure they would cause the engine running/not running issues.

The European forum noting a bad wheel speed sensor could cause the wonky speedometer stated that the wheel speed sensor was integrated into the hub so needed a new hub.

I don't know if that is the case. US hubs may be different so the speed sensor could be fixed without a hub replacement. The ABS wiring or connectors could be bad. There could be an issue with the computers.

Code reader will tell you which ABS sensor is reading poorly. Visually inspect the wiring and harness from the wheel to the computer. You can disconnect the cables, test circuit with an DMM, clean the contacts on both sides of the wiring and see if that helps.