03 cummins 5.9 IAT sensor ? cold starting issues.

[schiker]

A friend is having cold start issues on his 2003 Cummins 5.9. It doesn't want to start when its chilly. Will crank fine if plugged in when its ambient cold. I offered to help look at it Saturday.

Its probably one or both of the contactor/relay/solenoids feeding the air heater is my initial thought. I can probe the contactors/relays ok I think but would like to see if the IAT sensor has a resistance in correct ballpark range of temp. The 2003 + has a MAP/IAT combo.

I found this pinout and a good website for basic logic.

Can I measure the resistance of pins A to B and see the ohm's are similar to chart in the link for when to command air heater. ie below 60F aka 15K ohms.

Can you just unplug the IAT/Map sensor to command longest air heater time? I would undo wires and not burn out heater/kill batteries just if I need extended wait to start time to measure stuff or one try to see what happens.

Do you see any major logic change for the 2003 system? Do they measure any other air temps for when to cold start aid? I figure its the same logic control. Key on run power is supplied to relay ECM controls ground (if wait to start light relay should be pulled in).

Any quick tips?

How robust is the heater element?

Man I have to buy one of those power probe kits Will talks about!




http://dodgeram.org/tech/dsl/troubleshooting/Maniford_htr.htm#basics

 

[MrMarty51]

If there is another relay in the system with the same part nos then try switching them around.

 

[WarWagon]

it really doesn't need the air heater to start. You got other issues with a no start. Look at batteries, grounds, and the starter for cranking RPM being low. Also if the fan shorts out it won't start. Disconnect the fan at the lower radiator and see if it fires off. Then look at rail pressure : must be over 4K PSI before ECM will fire the injectors.

 

[schiker]

Chilly is relative not sure of problem temps low 30'sF ???? maybe a bit colder. He lived with it last year not driving it with cold mornings. He lives about 1-1/2 hours away. I remember he asked me about it last year but don't remember the temps. He is wanting to check it out before it gets cold this year. Remember it was only a problem when it was cold and having sat to get fully cold ~ 12 + hours sitting. Think it did not crank only a few times for him and not sure of temps. If he plugged in the block heater it started like normal if it had run in last few hours it would restart no problem w/o block heater when cold ambient?

I can at least see if the solenoids are pulling in and make sure the fuseable links are not open etc.

I think I can use a timing light in RPM mode and figure out the rpm its cranking at somehow what is typical range for a 5.9?

I might try to access info with carcode but I am not that good with it. I will really be poking around with it if I hook it up. Think I could find rail pressure with it (does ECM read it) ?

 

[THEFERMANATOR]

The cummins should start down to around 35 degrees relatively easily without the intake heater, but below 32 degrees good luck without fogging out the driveway(yes, it is that narrow of a window where they go from starting to not). They need 1500 psi to make the injectors pop. TheECM triggers them as soon as it has found itself in the firing order, but you need 1500-1800 psi to get enough differential pressure for them to open. I didn't do much with the common rail, but the vp44 trucks didn't care about intake air temp for grid heater operation. They worked off of coolant temp. Intake air temp was used for density calculations, and to defuel in case of intake air temps going to high. The #1 cause of no grid heaters was the fusible links burning through at the battery from battery acid getting on them because Chrysler set the charging voltage so friggen high on them. The solenoids go out sometimes, but are a pretty heavy duty setup. And I have never seen or heard of a grid heater burning out in one.

If you have sensors in question, I always reccomend checking them via a scan tool 1st so you can see what the controller is seeing instead of comparing ohms to a chart as ohms isn't everything since the ecm doesn't read ohms. The ecm sends a reference voltage signal to one side and a ground on the other side. The ecm reads the voltage present on the reference line, and that is how it reads a sensor. I've seen sensors ohm out correct read off because the thermistor was correct on ohms, but not good enough to pull the voltage down appropriately. I recently ran into this with a temp sender that wasfor a 2 watt circuit, but the sender had a 1.5 watt thermistor. Ohms were dead on, but the guage read low. So ohms isn't everything.

 

[schiker]

Good to know about sensor diagnosis. Not surprising as DMM's can easily fool you into thinking something is good ie when you get voltage or continuity but it can't support the current draw required. DMM's are usually only good for determining something is completely dead.

And that is about all I could do yesterday with limited time the "basics" of the system weren't dead. I measured continuity and very low ohms with no load through the fuseable links, heater element, and wires. I removed the relay trigger wires, unhooked the fuseable link from the battery, then triggered the relays manually with jumper wires and they clicked and I measured continuity across the relay.

It was about 63F degrees in the shop and the truck wasn't cold so I think all we had was the bulb check for air heater and no actual triggered air heater time to check operation. Unplugging the IAT sensor did not seem to trigger max heater time to check the operation either (dash glow light was same 2 second bulb check). So I am questioning the logic posted in the article. Could be some AND logic with coolant temp or some other logic tells the ECM to trigger air heater (had originally assumed like the 6.5 coolant temp triggered cold start aid but went with article).

Next I wanted to verify with key on run had power coming to relay control wires and only measured 3 something volts stray voltage ????? The other relay control wire measured continuity to ground. Again was a little confused by this if the ECM grounds for triggering the relays and it was grounded already. We looked for the fuse #9 in the write up I posted and could not find it. The article I linked says its at dash but his year truck has no dash fuses all appear to be under hood. I didn't see any 10 amp fuses blown.

So now looking for info on what triggers the relays for 2003 gen 3 if its different than article. Is it grounded and powers when needed????

Ran out of time but I thought about manually triggering relay's and measuring current draw to air heater looking for high amp draw to confirm the relays aren't burned or fusable links aren't compromised somehow. If I would have gotten 80+ something amp draw I would have said ok load wiring fine.

What would you test next time?

 

[WarWagon]

3v isn't stray voltage: it's a high resistance connection preventing the operation of something. You have a bad ground, fusible link, or connection. It's 12v or 0v on the solenoids to control them. Measure them with key on and no grid light lit. If it has 12v on the control wires then the ECM is grounding to turn on. 0v means the ECM is providing power.

 

[schiker]

This is a 2003 HO engine if that matters or are they all called HO.

So is this the correct logic for a 2003 see clip?

The picture with white and black wires going to relay's are my friends actual truck.

So I should get ground on the black wires all the time.

White wires should show either
0V no heater
12V activated (this is via the ECM key on run grid heater indicator on dash lit).

I should probably use a test light to see if its commanding grid heater.

I saw one person say take out the IAT/MAP sensor and stick it in glass of ice water. I wouldn't do water but a glass of ice and rag to cover to chill the sensor might be an idea.

Any other way to test it.

 

[WarWagon]

Not there, but, I feel you are looking too hard at the grid heaters themselves. The 5.9 will start down to 0 degrees without waiting on the grid heater. Let me suggest you look at the big picture that your probing of the heaters is showing you.

Survey says he needs a set of injectors due to excessive return rates from the same era of bad Duramax injectors. Watch the rail pressure while cranking cold. Below 4K on HPCR the ECM isn't going to fire the injectors. the 2003 had a lift pump (not flow on fail) on the side of the filter canister that's prone to failure: in tank pumps were the replacement, but, you can still get an improved design direct replacement.

You indicated a ground problem with 3 volts measured. 3 Volts is extreme on a 12v system. I ignore anything below 1v and 0.5v under a microscope when looking for problems. What exactly were you measuring and where was your ground point on the voltmeter? This is CRITICAL! But it may have zero to do with the heaters. You found a "high resistance" ground path. So was it battery cables if you grounded at the battery post, body ground if you grounded at the body, or ground location of the relay if you measured just the relay ground wire. If you have 3v at the solenoid ECM wire we need to assume the ECM was commanding it on. If the ECM wasn't commanding the heaters on you still have a ground problem and the voltage is looking for other ways to ground: voltage feeding back from the high resistance ground.

It's possible the ECM was commanding the heater "on" and the positive side has a high resistance connection only giving you 3v. For example the blower motor goes through the ignition switch and is known to melt both the connector and switch. No relay... Full current through the switch in good ole GM style.

I would load test each battery separately, disassemble the grounds esp the battery to engine, check the cables for internal corrosion, and clean every ground you can find. Note grounds above the batteries on the fender: both sides. The fender grounds are in the acid vapor area as @THEFERMANATOR mentioned from high charging voltages. Good luck keeping the tops of the batteries clean as the system likes 15v and is normal for a true temperature compensated charging with the temp sensor located under a battery.

2003 had 2 HP levels. HO not available in CA due to emissions, Normal with 5 speed and auto, HO that came with a NV5600 6 speed only. (The only trans that could take that power and maybe make it out of warranty.) Supposedly the 2003 was one of the best Dodge Diesels made lacking the TIPM krap, EGR by cam grind was the only emissions on the engine, best piston bowl design (later 6.7L years went back to it) thus it got the highest MPG.

Make sure he is changing the NV5600 oil often (30k miles) and running it a quart high as the syncromesh design sheers the oil to water viscosity.

 

[schiker]

You are probably correct age is a suspected issue in my mind. Yes battery strength, injectors, and cranking speed (healthy IP, fuel, no air etc) are important. The starting aid is for fast start, faster warm up, cold emissions, and immediate commute. But as engines age a little help starting is always better. Cranks fine if he plugs in the block heater. It is relatively easy to verify the heater is working and may be easy to fix with IAT sensor or connection cleaning etc if I can check the amp draw on it knowing the ECM is suppose to be commanding it. He says it sounds the same cranking when cold not like its cranking appreciably slower.

I had turned the key on got out of truck and walked to front he measured from the ECM wire that goes on the relay to ground post passenger side and measured the 3V. I said hmmf that doesn't seem right grid heater light is not on. The other relay was still hooked up wondered if that might have screwed with reading?????

A thought is we might rig up a manual button to command grid heater(s) and see if that gets him by until he wants to replace injectors etc.

 

[WarWagon]

I had turned the key on got out of truck and walked to front he measured from the ECM wire that goes on the relay to ground post passenger side and measured the 3V. I said hmmf that doesn't seem right grid heater light is not on. The other relay was still hooked up wondered if that might have screwed with reading?????

No.

Other things being on just make the bad connection look worse. The relays are BOTH for the grid heater: each relay has it's own element... You are now looking at a high resistance connection on the ground path anywhere from the solenoid to the battery post. When you crank the engine batteries can drop to 11v from the load then knock 3 or more volts off from the bad connection and S$#T doesn't work anymore at 8v. (Min spec during cranking a Cummins is 9v.) If the ECM is on (affected by) that connection it could quit working properly or shut down from the brown out. (Cranking may increase current on the bad connection and make the voltage drop even worse.)

Your troubleshooting has found a big problem, congrats. NOW FIX THE BAD GROUND!!!

Probe solenoid to engine, battery negative to engine... Find exactly what wire and or connection has the 3v across it.

 

[schiker]

I don't know which Relay is which.

Lets say it was Relay 2. Pin or wire 47 from ECM. Wire 56 at relay (?hard to read) unplugged at relay no load measured relative to battery post. I get 3V when the grid heater light is off on the dash is screwy but it doesn't seem like a bad ground. More its chaffed with a hot wire doesn't it (could be a loaded ground chaffed through and sharing path with wire 47/56)???? Shouldn't wire 56 be either ~0V or ~12V.

 

[MrMarty51]

Here is a link to relay wiring.
http://www.therangerstation.com/tech_library/relays.html

 

[WarWagon]

Pull the battery trays and look for acid damage to the wires below the trays. Yes, should be 0v or 12v on the ECM side of the relay and near 0V at all times on the ground side. They share a ground so it doesn't matter what relay as they both are grid heater.

Edit: it's possible the relay coil is shorted out : swap wires with the other relay and see if the same 3v follows the relay or ECM wire.