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Eric writes:
I read your plea for questions, so I'll lob you a softball. Why has my 2005 Maxima's TPS decided to randomly poop out on me after doing a warm start?
Specs: 2005 Nissan Maxima 6MT. 135,000 miles. Electronic throttle. Stock air intake + (new, put in the first time the TPS acted up 3K miles ago) K&N filter. The car's now on its third owner, having spent its whole life in Evansville, IN, Lexington, KY, and now Louisville, KY. At the rust belt's frayed fringe, I guess. No surface rust anywhere on the car, though. Electrically speaking, it's in good shape. (Save the rear ABS sensors… a rant for another day)
Relevant codes*: Throws a P2135 for sensor voltage being out of spec whenever it acts up.
Scenario: Drive the car a while to be fully in the operating temperature range. Turn the engine off. Wait for a long train to pass/run in and renew your driver's license/do some quick shopping, now turn on car. Car slow to start. Throttle goes into fail safe** (hold the pedal to the floor, wait a few seconds, revs rise slower than a DD15). Turn car off. Wait a second. Turn car on. Blip throttle, engine roars. You're back in business.
Attemped fixes: The mechanic at my work suggested I clean the MAF. I did that. He suggested I check the connector and clean it. It looks good, I sprayed some of the MAF cleaner on there, too. No luck, it still acts up. His newest suggestion is to follow the harness to the firewall and look for a pinch or something. That sounds like work to me, and I'm a pretty lazy guy, so…
My question is, how does a throttle position sensor go bad? It's way up high out of the way of muck from the road, so what's the deal? Specs state it should be between 0.36V and 4.75V (at full throttle), so it's not like there's some high current load burning it up. The problem is that I can't find an actual throttle position sensor in the Nissan parts diagrams, and I realllly don't want to spend $615 on a new throttle body (file away this nugget: try CourtesyParts.com, they're the best OEM retailer of Nissan parts I've found.).
Question 2: What're the chances that something's wrong with the harness? Why would it go away after a restart? (Yeah, that latter question is a crappy one)
*Other codes: Dreaded P0420 on the precats I installed 2 years/30,000 miles ago to treat the environment right and turn off the P0420. Also lit is the parking brake light, the traction control disabled light, the "your wheels are slipping/TCS engaged" light, and the ABS light. The car's upset that I snipped two fusible links in the engine bay to kill all power to the ABS actuator. Cough. That was about three months ago and is wholly separate from the throttle control.
**From the FSM:
"The ECM controls the electric throttle control actuator in regulating the throttle opening in order for the idle position to be within +10 degrees. The ECM controls the opening speed of the throttle to be slower than the normal condition. So, the acceleration will be poor." No, really!?PS: How's Sanjeev doing these days? He's been quiet for a while.
Sanjeev answers:
It's about time you people demanded my presence!
We know I don't respond with garbage like "ZOMG SON U SWAP LS4-FTW lest Panther Love because I'm a big stupid jerk in my First Generation Mark VIII"…or whatever he normally says. Wait, what's your problem again?
Sajeev answers:
While my arch nemesis with the far more common Indian name continues to disappoint, let's talk Nissan Maxima TPS. Engine code P2135 points to a problem with the drive by wire (i.e. no throttle cable) system, which is excellently described here. Long story short, there's a sensor on the go-pedal, another 1-2 more on the engine's intake throttle plate, an actuator for said plate, and some wiring to make it work.
The wiring could be bad/dirty/corroded/loose at either sensor, but odds are cleaning and checking won't cure the problem. There's a good chance one of these sensors went south. That's because anything that moves does indeed wear out: remember scratchy old records on the Hi Fi? That's the wear a seemingly non-moving sensor endures!
And lucky you: if the sensor on the throttle body side is bad, you get to replace the throttle assembly. Because that's how modern drive-by-wire systems work: yeah, how fun!
Do yourself a solid, read the above hyperlink. If the throttle body is bad and you're broke, consider a reman part instead of the original: they're about half the price. And since this is a 10-year-old machine, be ready for the worst…you will need a replacement throttle body. Hmm-kay? Yeeah.
photo courtesy: heatherpierceinc.com
Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you're in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.
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